Geo: Document Resync and Reverify individual and bulk actions

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Context

After rolling out the geo_registries_update_mutation FF and enabling the resync/reverify actions globally. We need to improve the documentation for https://docs.gitlab.com/ee/administration/geo/replication/troubleshooting.html#manually-retry-replication-or-verification as follows:

• Reflect that customers can resync and reverify blobs and repositories via the Admin UI. Indicating which versions started this support while keeping the existing instructions for older versions.
• Reflect that customers can resync all and reverify all blobs and repositories via the Admin UI. Indicating which versions started this support while keeping the existing instructions for older versions.
• Highlight the limitations. i.e: if object storage replication managed by CSP. The limitations are broadly described here: #415374 (This will be covered by the implementation instead).