Add postgres_foreign_keys.parent_oid, postgres_foreign_key.is_valid columns

What does this MR do and why?

Describe in detail what your merge request does and why.

Adds two new columns, parent_oid and is_valid to the postgres_foreign_keys view. These will be necessary for fixing list partitioning to support foreign keys.

This MR was split out of !104792, and will be the first of 4 MRs that encompass that functionality.

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