Improve migration squashing review process

Overview

I think there's some room to improve our migration squash review process. Usually, this kind of MR have a lot of diffs, what makes hard to validate all the changes.

Proposal

• Automate the process by validating the changes against the production DB - By detecting changes to init_structure.sql
• Generate an file (artifact) with diffs from production DB schema
• Update DB docs on how to review squash migrations MR's
  • Maybe focusing in some key points to review in this type of MR