[lib] Add a way of marking migrations as schema-changing

Summary:
When running the migrations check if any of them is marked as schema-changing.

https://linear.app/comm/issue/ENG-7493/add-a-way-of-marking-migrations-as-schema-changing

Depends on D12015

Test Plan: Add a log checking if schemaChanged is computed correctly. Add a migration without changesSchema and check if the value is false. Then add a migration that changesSchema and check if the value is true.

Reviewers: kamil, marcin, varun

Reviewed By: marcin

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12049