Create runbook-style documentation for a failover with two sites, single-node Geo, omnibus-managed database

Currently, the DR documentation is quite "jumpy". It would be great to provide a clear linear process for a simple failover, that includes all steps.

Proposal

Create/refactor documentation with the following structure:

• Failover with two sites, single-node Geo, omnibus-managed database
  • Preflight checks (listes)
  • Make primary unavailable
  • Promote secondary site to primary
  • Optional: Demote primary to secondary and add to new primary

This may not require that much work but ideally should focus on simplicity.