feat: biocommons admin endpoint to update group roles

[marius-mather]

Description

Group admin roles should now be set automatically when the database is populated. But in order to update existing ones, we need an API endpoint (accessible only to BioCommons admins)

Changes

• Add /biocommons-admin/groups/:group/set-admin-roles endpoint
• Unit tests

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]

Don't see any issues ...