Add -t option to populate managed modules using GitHub's repository topics

[joestump]

GitHub supports tagging repositories with "topics". This PR leverages this functionality to populate a list of managed modules rather than having to manually maintain managed_modules.yml.

This allows teams to add the topic ruby to a GitHub repository and then use the -t ruby option in their Ruby Modulesync CI/CD job to grab all of the repositories to sync.

[bittner]

Interesting! This sounds like driven by the same idea we had for managing GitLab projects with their projects topics. :+1:

See our Python CLI package concierge-cli on PyPI for reference.