Document how to use dependency groups in developer/contributor guides

[leofang]

It would be nice to document how this works for internal/external developers as well as QA.

Originally posted by @leofang in #995 (comment)

[tylergibbs1]

I would like to work on this.

Proposed approach: document the repository dependency groups in the contributor/developer guidance, including the commands for listing and installing them and when each group is appropriate. I’ll keep the change scoped to the existing uv workflow and validate the affected documentation locally. Could a maintainer assign this issue to me if that scope looks right?