MariaDB/Primary switchover

Prerequisites shared for all MW sections

(The following points apply to planned MW switchovers only, skip directly to section links below when responding to an incident)

Create a switchover task (see an example task or use the script to auto generate the MW switchover task
Schedule the switchover for one of the two weekly MW maintenance windows (check other open tasks and the deployment calendar for possible conflicts):
- Tuesday at 6:00 AM UTC
- Thursday at 6:00 AM UTC
Obtain explicit availability confirmation (over any channel) from at least one other person and add them to the task using the "Other assignee" field
Send a calendar invite to sre-data-persistence@
Add a user-notice Phabricator tag to the task for CRS's visibility