Summary:
Adding more logging to HA promotion, demotion, and switching prometheus config.

Also changed the backup size metric to correctly maintain precision when converting to mb.

Test Plan:
HA setup and promotion, check logs.

Verify backup metric not zero on new YBA

Reviewers: dshubin, sanketh

Reviewed By: dshubin

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D37674