Improve discoverability of the pydocstyle rules as per the selected convention

[dhruvmanila]

If a user has D in the rule selection, the rules that are actually selected depends on the docstring convention that's chosen. Currently, this information only lives at the bottom of this FAQ section: https://docs.astral.sh/ruff/faq/#does-ruff-support-numpy-or-google-style-docstrings. It would be useful to have this visible in an obvious place for which I see two options:

1. ruff.lint.pydocstyle.convention section
2. For each of the Dxxx rule page, specify how setting the lint.pydocstyle.convention may affect the selection of this rule

I think I'd prefer option (1) as the documentation is in a single place instead of distributed across multiple rule pages.