Allow boolean FSDP options in fsdp_config
Author: helloworld1
Pull request: yes
Labels: name: PyTorch FSDP

# What does this PR do?
When using the fsdp_config option, it must be passed in as string for some configuration.
The following config will result in crash
```
{
  "limit_all_gathers": true,
  "backward_prefetch": "backward_pre",
  "use_orig_params": true,
  "cpu_ram_efficient_loading": true
}
```

Error:
```
Traceback (most recent call last):
  File "/home/jobuser/training.py", line 107, in <module>
    main()
  File "/home/jobuser/training.py", line 40, in main
    training_args, custom_args = parser.parse_args_into_dataclasses()
  File "/home/jobuser/.local/lib/python3.10/site-packages/transformers/hf_argparser.py", line 338, in parse_args_into_dataclasses
    obj = dtype(**inputs)
  File "<string>", line 121, in __init__
  File "/home/jobuser/.local/lib/python3.10/site-packages/transformers/training_args.py", line 1691, in __post_init__
    os.environ[f"{prefix}USE_ORIG_PARAMS"] = self.fsdp_config.get("use_orig_params", "true")
  File "/export/apps/python/3.10/lib/python3.10/os.py", line 684, in __setitem__
    value = self.encodevalue(value)
  File "/export/apps/python/3.10/lib/python3.10/os.py", line 756, in encode
    raise TypeError("str expected, not %s" % type(value).__name__)
TypeError: str expected, not bool
```

This PR fixed the issue by casting the config value to `str`.


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