Geo: Fix consuming events of blobs that should not be synced

What does this MR do?

Selective sync settings, object storage settings, etc are supposed to prevent particular records from being synced.

1. The backfill/cleanup process (RegistryConsistencyWorker) already adheres to these settings by depending on a properly written replicables_for_geo_node scope which is specific to each Model.
2. But we also need to make sure that events do not attempt to sync things that should not be synced.

This MR accomplishes 2) above, in a DRY way, by reusing replicables_for_geo_node.

• The first commit is the behavior change.
• The next few commits are refactors organizing the tests.
• Then I added the test for the new method.

Resolves #224634 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.