Handle undefined table 'application_settings' for registry database.

patroni-registry does not have the application_settings table like main/ci/sec. We need to handle this case (in addition to the undefined column case for ci and sec (once sec table truncation occurs)).

Ideally we could target specific databases in gitlab-helmfiles when we roll out scraper configs, but that doesn't seem possible currently. As a workaround to adding an empty application_settings table to registry, we shouldn't assume the table exists and handle that case appropriately.

Note: This is not a codebase I'm intimately familiar with, so please scrutinize with care and I'm certainly open to any and all suggestions for improvements.