Improve file verification status presentation in replication summary table

Proposal

The file verification status in the replication summary table is confusing some users. It's not clear what the -% means. We should show N/A with a tooltip why this is N/A for their particular configuration.

In future when we do introduce object storage verification that works alongside GitLab-managed object storage replication, this will have meaningful values. However, if the customer chooses to use the provider's objects storage replication this will continue to be N/A.