Cache path lookups for namespaces [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Ensures that path lookups for projects/namespaces/groups are cached, both for a request and until the records are updated.

This introduces a bunch of early returns to make as much use of preloaded data as possible before defaulting to a cache wrapping the original code.

This will heavily reduce the impact of one of our top 10 queries by volume.

Also includes the first caching utility method in Gitlab::Cache that I'm going to expand upon later.

Resolves #325334 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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