Discussion/review of the database schema and migrations
Context
As part of &2313 (closed), we're working in moving the registry metadata from the filesystem into a PostgreSQL database. This will be a separate database, owned by the registry (see #93 (closed) and https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/10109 for context).
The initial version of the database schema was designed and discussed in gitlab#207147 (closed), and we have made several changes since then. This issue is to review and discuss the current database schema with the Database team, looking for opportunities to improve the design, before we move on to the next step which is implementing offline and online garbage collection, using the metadata database.