Adding `top_k` argument to `text-classification` pipeline. (#17606)
* Adding `top_k` and `sort` arguments to `text-classification` pipeline.
- Deprecate `return_all_scores` as `top_k` is more uniform with other
pipelines, and a superset of what `return_all_scores` can do.
BC is maintained though.
`return_all_scores=True` -> `top_k=None`
`return_all_scores=False` -> `top_k=1`
- Using `top_k` will imply sorting the results, but using no argument
will keep the results unsorted for backward compatibility.
* Remove `sort`.
* Fixing the test.
* Remove bad doc.