Move recursive namespace query to INNER JOIN [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This MR moves the recursive namespace CTE query within Namespace#all_projects from IN (QUERY) to INNER JOIN (QUERY).

Plans, and query examples: https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12791#note_526772331

Note the change is behind a FF: recursive_namespace_lookup_as_inner_join

Does this MR meet the acceptance criteria?

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