FDW status of Geo secondaries in Geo Node screen

What does this MR do?

• Refactors FDW methods in Gitlab::Geo and move to Gitlab::Geo::Fdw
• Add additional methods in Gitlab::Geo::Fdw to retrieve information
• Exposes extra information in status API
• Replicated checks to the SystemChecks

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

Why was this MR needed?

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

What are the relevant issue numbers?

Closes #4297 (closed)