hooks: sqlalchemy: collect plugins and dialects via entry-points

[rokm]

Have sqlalchemy hook collect all dialects and plugins that are registered via sqlalchemy.dialects and sqlalchemy.plugins entry-points. This ensures collection of 3rd party dialects and plugins that may be available in the build environment (e.g., ibm-db-sa).

Closes #3518.

[bwoodsend]

I'm starting to wonder if perhaps we should try to scan for entrypoint iterating code like we do for importlib.metadata.distribution("xyz")? I originally dismissed the idea since it would make packages with entrypoints hoover up dependencies instead of encouraging users to pick only the providers they use but our go-to strategy has ended up being to just collect them all without thought.

[rokm]

I'm starting to wonder if perhaps we should try to scan for entrypoint iterating code like we do for importlib.metadata.distribution("xyz")? I originally dismissed the idea since it would make packages with entrypoints hoover up dependencies instead of encouraging users to pick only the providers they use but our go-to strategy has ended up being to just collect them all without thought.

Hmm, yeah, perhaps we should. While I don't particularly mind dealing with this via hooks on per-package basis, it is true that for the lack of better strategy being available, those hooks end up collecting all available entry-points, and we might as well automate that part.