GEO: clarify Geo HA DR documentation

Summary

Geo HA Disaster Recovery documentation could use some clarification.

When promoting the secondary to primary, we need to add a note to comment out geo_postgresql['enable'] = true or set it to false.

May also be helpful to clarify that promoting the secondary to primary essentially disables Geo. There is some confusion around needing to set geo_primary_role['enable'] = true. This does not need set until you want to add secondary nodes to the newly promoted master.

Links

Customer ticket -> https://gitlab.zendesk.com/agent/tickets/96279 (internal)