Fix group blobs search permissions and update specs

What does this MR do and why?

Found during marking backfill_traversal_ids_to_blobs_and_wiki_blobs migration as obsolete in !118111 (merged)

• Add migration check to visibility specs for when backfill_traversal_ids_to_blobs_and_wiki_blobs migration is not completed
• Add project level check to group queries using traversal ids for blobs
• Small refactor to allow code re-use (I want to refactor this code further but will do in a follow up MR to keep this one small)

Screenshots or screen recordings

N/A

How to set up and validate locally

I'm relying upon the visibility specs which are more comprehensive than a manual test to test this change

MR acceptance checklist

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