CI docs generation is broken

[dvrogozh]

As can be seen in github actions ci, https://github.com/pytorch/examples/actions/workflows/doc-build.yml is broken in last few commits. That's unrelated to any actual commits in the repo and happenned due to updates on 3rd party sides (github actions runners and sphinx). First failure in (https://github.com/pytorch/examples/actions/runs/13041502252/job/36384208905):

E: Package 'python-setuptools' has no installation candidate

Unfortunately that's just a tip of the iceberg. Above error is apt-get issue and can be easily fixed with installing python3-setuptools. This however will uncover next issue:

Sphinx version error:
The sphinxcontrib.applehelp extension used by this project needs at least Sphinx v5.0; it therefore cannot be built with this version.

That's sphinx-doc/sphinx#11890. If we will change requirement to spinx>=5, we will further step into:

An error happened in rendering the page index.
Reason: UndefinedError("'style' is undefined")

As of now I did not identify the fix with my few trivial attempts. This needs some work.

@atalman, @msaroufim : by any chance, maybe you've met these spinx related versioning issues in other pytorch projects and can point me to where I can borrow a fix?

[dvrogozh]

The following PR has addressed the build issue (thank you, @jafraustro):

• Update doc-build.yml and requirements for documentation build #1333

And we discuss additional improvements on top in (thank you, @soot-bit):

• This PR Improve docs build ci  #1336