Geo: Create a single command to promote a Geo secondary site

Problem to solve

Promoting a Geo secondary site with multiple nodes requires manual editing of gitlab.rb on each node.

Proposal

• gitlab-ctl geo promote detects omnibus-managed services running in the secondary node that need to be promoted
• gitlab-ctl geo promote changes configuration to primary

Validates

• Validate failing over to a secondary site with a single node;
• Validate failing over to a secondary site with multiple nodes;
• Validate failing over to a secondary node with a Patroni standby cluster;