Removing run_pl_glue.py from text classification docs, include run_xnli.py & run_tf_text_classification.py

[cbjuan]

What does this PR do?

Since run_pl_glue.py is not part of text-classification examples after #9010, this PR removes it from the text-classification docs. Also, it adds run_xnli.py and run_tf_text_classification.py scripts, which are in that folder now.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

@sgugger may be interested in the PR, he's responsible for docs and the author of #9010

[sgugger]

Good catch! To make each version of the documentation point to the examples that go with it, the links should also be like this:

:prefix-link:`run_glue <examples/text-classification/run_glue.py>`__

This way the master will be replaced by the tag of the release when in the docs of a specific version.

[cbjuan]

Sure! Change applied

[sgugger]

Thanks!

One last thing, could you run make style on your branch so that the formatting is applied?

[cbjuan]

Done, command make style applied. Thanks for the guidance

[cbjuan]

Build still not succeeding. I will check

[sgugger]

Ah yes, those links don't need the underscores! Good catch and sorry for giving you the wrong example to follow. Just waiting for the last tests and we can merge :-)

[cbjuan]

No worries, @sgugger. Thanks for the guidance :)