Store MD5 hash of each migration

We shall store MD5 of each migration file and we shall check if checksums of every migration matches on each migration UP / DOWN. That is necessary to avoid inconsistent schema changes when plugin developer changes existing migrations (which is forbidden by the common sense but not technically impossible)

DoD:

• RFC updated to reflect hash checks
• Hash checks implemented

RFC discussion: https://docs.google.com/document/d/1QMFXWhrSJ9VLFNX-jayHCzG8jk01VwtOuTOzooBBsOA/edit?disco=AAABLZaHC4o