Add status about replication slots to Geo Primary status screen

What does this MR do?

Note: this MR is being implemented by @kushalpandya in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3902

Building off of MR https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3621, add the replication status to the Geo Nodes status screen.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The following stats were added to the GeoNodeStatus model for the primary node:

replication_slots_count
replication_slots_used_count
replication_slots_max_retained_wal_bytes

These should be added to the Geo Node Status screen in the Primary section, under an Advanced accordion like the Secondary node.

replication_slots_count and replication_slots_used_count should be presented as a progress bar, while the replication_slots_max_retained_wal_bytes can be a field formatted as MB.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan

What are the relevant issue numbers?

Closes #4179 (closed)