Database page unusable after removing all configured roles

[pavish]

Description

• Create a new database
• Notice that the admin account is added as a collaborator, and we have a configured role for 'Mathesar'.
• Remove the Configured Role 'mathesar'.
• Notice that the data is still visible due to cache. Go back to the Home page and enter the database again (or refresh the page).
• Notice the error: DoesNotExist: UserDatabaseRoleMap matching query does not exist
• We are no longer able to configure any new role - Role Configuration page is unusable.
• We are not able to query existing roles - Roles page is unusable.
• We cannot add the admin back as a Collaborator since there are no roles configured.