Add `Migration[2.0]` that enforces `restrict_gitlab_migration`

What does this MR do and why?

This is based on: !73756 (merged) and require the former to be merged first.

This implements a new migration version and validates if correct migration version is used depending on a cutoff points.

This allows to enforce a usage of a new restrict_gitlab_migration.

The usage of Migration[2.0] is still opt-in, with 1.0 being default for time being.

MR acceptance checklist

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