WIP: Move AWS Instance Profile resolution to ApplicationSetting to avoid AWS throttling

What does this MR do?

Moves #resolve_aws_credentials to ApplicationSetting and memoizes it so AWS instance profile credentials aren't resolved once per project and instead end up resolving once per sidekiq worker.

TODO:

• tests

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

• Is there a need to detect when instance profile creds are no longer valid to look them up again? It doesn't seem necessary from what I've been able to gather since it's only used in sidekiq workers, which will reload the entire app anyways.

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
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #4334 (closed)