[3.1.1 backport] Improve handling for deleted collection

If a database is created with access to collection A, and then the collection is deleted on Couchbase Server, we need a way to modify the SG database to remove that collection.

Proposed fix would be to start the database in offline mode in this scenario (in conjunction with the enhancements in CBG-2909) so that the config can be modified.  Should show an error status when trying to request the /db/ endpoint.

Priority depends on validation of existing handling.