Investigate migrating documentation to Stardoc

[jayconrod]

Stardoc is a documentation generator for Bazel rules, providers, and other definitions.

Currently, Gazelle documentation is maintained separately from the implementation, so it's easy for it to drift.

We should investigate whether Stardoc is a viable replacement for the current documentation. If it is, we should migrate the current documentation to generated Stardoc.

Analogous rules_go issue bazel-contrib/rules_go#762.

[alexeagle]

@achew22 now that we've committed to having some markdown in the repository, for documentation that's output by stardoc, what do you think about having a mix of rst and markdown in the long-term? Or should I also run the remaining docs through something like pandoc to translate them to markdown as well so there's only one markup language? IMO we should do the latter.

[achew22]

I think that's a great idea. Let's leave this issue open to group all the work that needs to be done, but I appreciate all the work. Thank you!