Extend `gitlab_schema` to understand partitioned and deleted tables

What does this MR do and why?

We seem to analyse data sources in a number of different formats that are outside of currently visible tables (as defined by gitlab_schema.yml).

These tables include:

• Rails accessing pg_* catalog tables
• Rails accessing information_schema.* catalog tables
• GitLab Rails accessing and deleting data from partitioned tables
• GitLab Rails in specs accessing deleted tables as they are referenced by some migrations

This is a portion taken from !71540 (closed) responsible for table to schema classification.

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