Add task to fix migrations for 15.11 upgrades

What does this MR do and why?

Add task to fix migrations for 15.11 upgrades

This is specific to 15.11.x - a migration squash that is present in 15.11.0-15.11.2 (inclusive) removed a crucial migration that was chronologically out of order from the squash point which introduced an error. Then the migration squash was reverted for 15.11.3, which means that users upgrading from an earlier 15.11 would see new migrations that haven't run yet, and an attempt to run them would error out.

This rake task detects that condition and patches in the necessary timestamps.

How to set up and validate locally

To reviewer: I suggest trying to upgrade from 15.11.0 - 15.11.2 to this branch:

git checkout v15.11.0-ee
bundle exec db:drop db:setup
git checkout 411490-migrations-fix
bundle exec db:migrate

This process may be repeated with 15.11.1, 15.11.2, 15.11.3, 15.11.4.

Related to: #411490 (closed)

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