Release Geo: Treat missing blobs as sync failed

What does this MR do and why?

Describe in detail what your merge request does and why.

Release the behavior change "Geo: Treat missing blobs as sync failed".

• !76801 (merged)
• !77203 (merged)
• !77208 (merged)

Related to #348745 (closed) and #348590 (closed)

I am enabling the feature flag by default and not removing the feature flag so that the feature flag can be available for at least one whole release to be able to revert the behavior in an emergency.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Set up Geo
2. Create an issue and attach an image to the description
3. In Rails console on the Geo primary site: File.unlink(Upload.last.absolute_path)
4. In Rails console on the Geo secondary site: r = Upload.last.replicator; r.send(:download); r.registry.last_sync_failure
5. That last command should output "The file is missing on the Geo primary site"
6. Visit /admin/geo/nodes. You should see a new failure in the Uploads replication progress bar for your secondary site.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.