Fix indexes for project_repository_states

What does this MR do?

We currently have index

add_index "project_repository_states", ["project_id"], name: "idx_repository_states_outdated_checksums", where: "(((repository_verification_checksum IS NULL) AND (last_repository_verification_failure IS NULL)) OR ((wiki_verification_checksum IS NULL) AND (last_wiki_verification_failure IS NULL)))", using: :btree

which is not used when we use only wiki or repository related fields alone, like here:

SELECT COUNT(*) FROM "projects" INNER JOIN "project_repository_states" ON "project_repository_states"."project_id" = "projects"."id" WHERE ("project_repository_states"."repository_verification_checksum" IS NOT NULL) AND "project_repository_states"."last_repository_verification_failure" IS NULL;

I'm not deleting the old index yet as it's used in some queries. I think we need to defer it for the next release.

@yorickpeterse WDYT?

I only tested this on my local database which is not accurate at all. How can we EXPLAIN ANALYZE it @yorickpeterse ?

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• Conform by the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
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• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?