Geo: Provide list of manual checks with link to documentation

Problem to solve

https://docs.gitlab.com/ee/administration/geo/disaster_recovery/planned_failover.html#preflight-checks lists a number of preflight checks that needs to be performed. When running gitlab-ctl promote-to-primary-node the user may not be aware that these are required.

Proposal

• Include a list of non-automated preflight checks in gitlab-ctl promote-to-primary-node and print list when running
• Provide link to documentation
• Make user affirm that they've done all manual preflight checks
• Commandline option to indicate manual checks were performed e.g. gitlab-ctl promote-to-primary-node --manual-checks-ok

Mock up:

Ensure you have completed the following manual preflight checks:
- Review configuration of each secondary node
- Check that secrets match between nodes
- ....

Please read https://docs.gitlab.com/ee/administration/geo/disaster_recovery/planned_failover.html#preflight-checks

Did you perform all manual preflight checks (YES/NO)?
--> YES continue
--> NO
ERROR: Manual preflight checks were not performed!
Please read https://docs.gitlab.com/ee/administration/geo/disaster_recovery/planned_failover.html#preflight-checks