Fail build when the structure.sql is changed, and no migration is added

Context:

We had a MR merged where we removed some indexes from structure.sql by mistake (during rebase). This can create a big issue because new self-host customers will use this file to generate the database schema.

Deliverables:

• The pipeline should fail when the structure.sql is changed, and no migration is added.
• There's a way to override this in circumstances where this behavior is necessary.