chore: refactor group request endpoint (AAI-462)

[marius-mather]

Description

AAI-462: move the endpoint for requesting group access under the user router.

While doing this I noticed we had an outdated group approval endpoint, so I've removed it as part of this change.

Changes

• Move /biocommons/groups/request to /me/groups/request
• Remove outdated /biocommons/groups/approve endpoint
• Remove biocommons_groups router now that it's unused
• Move email functions to a common module

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)
• For any new secrets, I have updated the shared spreadsheet and the GitHub Secrets.

How to Test Manually (if necessary)

Run uv run pytest

[amandazhuyilan]

Could not be better - thanks for the change