Validate that connection accesses valid tables in migrations

What does this MR do and why?

This validator is very similar to cross-join validator that is part of specs. The purpose here is to ensure that when running migration code we never do not mis-access databases.

1. This is effectively enabled only when running Migration[2.0]
2. This effectively allows to discover broken usage of #finalize of background migrations that misuses connections and prevent data corruption

Related work:

• #358430 (closed) - describes a general rollout process of Migration[2.0]
• #362268 (closed) - it is effectively part of that, to ensure that if operation misusing connection is run it is discovered and forbid
• !87412 (merged) - the fix to allow #finalize of BM to work properly

MR acceptance checklist

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