get_dataset_default_config_name docstring

fix https://github.com/huggingface/datasets/pull/6722

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6723). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.005658 / 0.011353 (-0.005694) | 0.003883 / 0.011008 (-0.007125) | 0.064007 / 0.038508 (0.025499) | 0.030370 / 0.023109 (0.007261) | 0.246677 / 0.275898 (-0.029221) | 0.270846 / 0.323480 (-0.052634) | 0.003102 / 0.007986 (-0.004884) | 0.002931 / 0.004328 (-0.001397) | 0.049446 / 0.004250 (0.045196) | 0.043555 / 0.037052 (0.006503) | 0.261810 / 0.258489 (0.003321) | 0.289705 / 0.293841 (-0.004136) | 0.028676 / 0.128546 (-0.099870) | 0.010778 / 0.075646 (-0.064868) | 0.210604 / 0.419271 (-0.208667) | 0.035987 / 0.043533 (-0.007546) | 0.248034 / 0.255139 (-0.007105) | 0.265019 / 0.283200 (-0.018181) | 0.018522 / 0.141683 (-0.123161) | 1.096364 / 1.452155 (-0.355791) | 1.152750 / 1.492716 (-0.339966) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.093987 / 0.018006 (0.075981) | 0.306143 / 0.000490 (0.305653) | 0.000218 / 0.000200 (0.000018) | 0.000045 / 0.000054 (-0.000009) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.018727 / 0.037411 (-0.018685) | 0.061983 / 0.014526 (0.047457) | 0.074254 / 0.176557 (-0.102303) | 0.121256 / 0.737135 (-0.615880) | 0.076756 / 0.296338 (-0.219582) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.278824 / 0.215209 (0.063615) | 2.815960 / 2.077655 (0.738305) | 1.472946 / 1.504120 (-0.031174) | 1.349722 / 1.541195 (-0.191473) | 1.327844 / 1.468490 (-0.140646) | 0.574964 / 4.584777 (-4.009813) | 2.403458 / 3.745712 (-1.342254) | 2.769293 / 5.269862 (-2.500569) | 1.736970 / 4.565676 (-2.828706) | 0.063144 / 0.424275 (-0.361131) | 0.004983 / 0.007607 (-0.002625) | 0.331212 / 0.226044 (0.105168) | 3.231496 / 2.268929 (0.962567) | 1.798487 / 55.444624 (-53.646138) | 1.523010 / 6.876477 (-5.353467) | 1.559973 / 2.142072 (-0.582099) | 0.657036 / 4.805227 (-4.148191) | 0.119084 / 6.500664 (-6.381580) | 0.042982 / 0.075469 (-0.032487) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.976433 / 1.841788 (-0.865355) | 11.475946 / 8.074308 (3.401638) | 9.339369 / 10.191392 (-0.852023) | 0.141761 / 0.680424 (-0.538662) | 0.014506 / 0.534201 (-0.519695) | 0.289944 / 0.579283 (-0.289340) | 0.273667 / 0.434364 (-0.160697) | 0.326682 / 0.540337 (-0.213655) | 0.458946 / 1.386936 (-0.927990) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.005194 / 0.011353 (-0.006159) | 0.003713 / 0.011008 (-0.007295) | 0.049297 / 0.038508 (0.010789) | 0.029723 / 0.023109 (0.006614) | 0.278664 / 0.275898 (0.002766) | 0.296387 / 0.323480 (-0.027093) | 0.004215 / 0.007986 (-0.003771) | 0.002680 / 0.004328 (-0.001648) | 0.048276 / 0.004250 (0.044025) | 0.044454 / 0.037052 (0.007402) | 0.290510 / 0.258489 (0.032021) | 0.319028 / 0.293841 (0.025187) | 0.029177 / 0.128546 (-0.099369) | 0.010361 / 0.075646 (-0.065285) | 0.056993 / 0.419271 (-0.362279) | 0.050765 / 0.043533 (0.007232) | 0.278234 / 0.255139 (0.023095) | 0.295848 / 0.283200 (0.012649) | 0.018776 / 0.141683 (-0.122906) | 1.134866 / 1.452155 (-0.317288) | 1.204083 / 1.492716 (-0.288634) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.094397 / 0.018006 (0.076391) | 0.304693 / 0.000490 (0.304203) | 0.000207 / 0.000200 (0.000007) | 0.000044 / 0.000054 (-0.000010) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.021322 / 0.037411 (-0.016090) | 0.075384 / 0.014526 (0.060859) | 0.086961 / 0.176557 (-0.089596) | 0.124424 / 0.737135 (-0.612711) | 0.087802 / 0.296338 (-0.208536) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.305542 / 0.215209 (0.090333) | 2.980678 / 2.077655 (0.903023) | 1.632348 / 1.504120 (0.128228) | 1.501466 / 1.541195 (-0.039728) | 1.517681 / 1.468490 (0.049191) | 0.579318 / 4.584777 (-4.005459) | 2.460734 / 3.745712 (-1.284978) | 2.650164 / 5.269862 (-2.619697) | 1.752061 / 4.565676 (-2.813615) | 0.064561 / 0.424275 (-0.359714) | 0.005097 / 0.007607 (-0.002510) | 0.359613 / 0.226044 (0.133569) | 3.518549 / 2.268929 (1.249620) | 1.962575 / 55.444624 (-53.482050) | 1.686108 / 6.876477 (-5.190369) | 1.787873 / 2.142072 (-0.354199) | 0.653715 / 4.805227 (-4.151512) | 0.117617 / 6.500664 (-6.383048) | 0.040359 / 0.075469 (-0.035110) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.021533 / 1.841788 (-0.820255) | 11.974817 / 8.074308 (3.900509) | 10.073530 / 10.191392 (-0.117862) | 0.141477 / 0.680424 (-0.538947) | 0.015081 / 0.534201 (-0.519120) | 0.292622 / 0.579283 (-0.286661) | 0.291043 / 0.434364 (-0.143321) | 0.347822 / 0.540337 (-0.192516) | 0.443647 / 1.386936 (-0.943289) |

</details>
</details>

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