docs: fix profiler docstring (#55750)
Summary:
Description:
- change the docstrings for profiler module as per google docstring
- add link to `torch.autograd` module
- document `ProfilerAction` and `ProfilerActivity`
https://12292060-65600975-gh.circle-artifacts.com/0/docs/profiler.html
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55750
Reviewed By: yinghai
Differential Revision: D27725494
Pulled By: ngimel
fbshipit-source-id: 32d0a18e274a871ac712b28b61ba63eb08299a03
