Automated indexer project tracking based on OSV.dev advisories

**Is your feature request related to a problem? Please describe.**
Indexer misses repositories publishing new C/C++ advisories that previously didn't exist in OSV.dev.
**Describe the solution you'd like**
By using OSV.dev advisories as a source of github repositories to index, we can always be up to date with indexer converage.

**Describe alternatives you've considered**
Keep the config bucket updated with a regular cron that checks new repositories. This doesn't provide much benefit over directly using the information contained in OSV.dev.