Geo: Secondary fails to replicate when using Hybrid Primary

Found during testing whilst using a 10k Hybrid Environment for the primary site and a 3k Omnibus Secondary.

Several issues arise during the initial Geo setup process, I'll list out below each issue below.

Relates to https://gitlab.com/gitlab-org/quality/gitlab-environment-toolkit-configs/staging-ref/-/issues/49

Proposal

• Update the Ref Arch setup docs for 10k, and up. Instruct sysadmins to over provision the site and increase the memory available to the Postgres nodes.
• In Geo Troubleshooting, add a section, with relevant error messages to make it searchable, and then instruct sysadmins to over provision the site and increase the memory available to the Postgres nodes.
• Cross link where helpful.