Geo: Migrate feature flagged settings to database

Proposal

From the discussion in #280581 (comment 444378383) about how to move away from feature flags to enable/disable replication for data types:

1. Add database settings for feature flagged replicables with a migration that defaults the setting to whatever the feature flag is set to.
2. Refactor to use the settings instead of feature flag.

Then follow up with #215475 (closed) to allow toggling of replication in the UI.