WIP: Resolve "Geo: Inconsistent database replication status when Wal-E streaming is in use"

What does this MR do?

In lieu of a better way to actually determine if replication is working, we'll reduce it to the check that replication is setup by way of having the secondary database in read only/recovery mode, which is already checked by the line

        return 'The Geo node has a database that is not configured for streaming replication with the primary node.' unless self.database_secondary?

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

Why was this MR needed?

As mentioned in the issue, we're seeing the message The Geo node does not appear to be replicating the database from the primary node on the Geo secondary in production (gprd). This is triggered by the line

        return 'The Geo node does not appear to be replicating the database from the primary node.' if Gitlab::Database.pg_stat_wal_receiver_supported? && !self.streaming_active?

in https://gitlab.com/gitlab-org/gitlab-ee/blob/master/ee/lib/gitlab/geo/health_check.rb even though replication is in fact working.

This is what is seen in the secondary console:

Gitlab::Geo::HealthCheck.streaming_active?
=> false
Gitlab::Database.pg_stat_wal_receiver_supported?
=> true

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
• Conforms to the code review guidelines
  • [-] Has been reviewed by a UX Designer
  • [-] Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • [-] Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [-] Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• [-] 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
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #5933 (closed)