Summary: In D41363 we changed the unit of the HA standby alert to be minutes to better reflect HA config set up so there is no conversion necessary. This diff adds the migration to actually change alert from existing second unit to minute, also converting the value from its second value to minute value.

Test Plan: Run migration locally, ensure new alert configured based on old alert

Reviewers: nsingh, amalyshev

Reviewed By: nsingh, amalyshev

Subscribers: sanketh, yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D41630