adding functionality to iterate pipelines over sentence pairs when using dataset
Author: rohit1998
Pull request: yes

# What does this PR do?

This PR adds a new torch data set class to pt_utils.py that helps with using pipelines and datasets for sentence pair tasks.
Usage can be simply like

```
dataset = Dataset.from_pandas(dataset_df[['sentence1', 'sentence2']])
pipe = pipeline('text-classification', model=args.input_path_model, device=0, num_workers=4)
result = list(tqdm(pipe(KeyPairDataset(dataset, 'sentence1', 'sentence2'), batch_size=32), total=len(dataset)))

```
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Fixes # (issue)
#19660

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

@Narsil , please have a look.