Geo: Create command for pre-flight checks only

Problem to solve

When integrating the preflight checks with gitlab-ctl promote-to-primary-node every time this command gets issued, a promotion sequence will be run after the preflight checks by default. This may not be desirable as a systems administrator may only be interested in running preflight checks as a dry run.

Proposal

• Implement a command promote-pre-flight-checks that will only run the preflight section of the command line tool
• Include this command in promote-to-primary