Geo Replicables: Add single replicable item view

What does this MR do and why?

It adds:

• a view for displaying information about a single replicable object;
• a route to access the view;
• a controller to get the replicable data as well as checking permissions;
• tests for the above.

This is to create a view that allows users to "dig into" a single replicable item's details: &16249 (closed) as defined in Issue #509349 (closed)

References

Issue #509349 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. Select the type of replicator you'd like to investigate. Example: Projects::WikiRepository.
2. Make sure there's a record of this type locally and get its ID. For example, in the Rails console: ::Projects::WikiRepository.first.id
3. Get the pluralize name for this replicator. In Rails console: Geo::ProjectWikiRepositoryReplicator.replicable_name_plural
4. Enable the feature flag: Feature.enable(:geo_replicables_show_view)
5. Navigate to: /admin/geo/sites/2/replication/<pluralized name>/<model_record_id>. The model_record_id would be the ID you found in step 2. ⚠️ the page is empty. The UI will be built later on.

Related to #509349 (closed)