Move frontend ~/artifacts to ~/ci/artifacts

What does this MR do and why?

For verify-stage#426 (closed), verify-stage#422 (closed), #393864 (closed)

We want to require verify domain expert approval to changes to the artifacts page javascript/vue code, so it needs to be covered by the [Verify] rules in our CODEOWNERS file. We can do this by moving this code into a ci subfolder to make it match the /**/app/**/ci/ pattern.

Screenshots or screen recordings

No UI changes are expected

How to set up and validate locally

1. echo "Feature.enable(:artifacts_management_page)" | bundle exec rails console
2. git checkout move-artifacts-app-directory-inside-ci-directory
3. navigate to a project, and in the sidebar select CI/CD => Artifacts
4. artifacts from the project's pipelines should appear as normal

to see this page in the review app

https://gitlab-review-move-artif-6do7iw.gitlab-review.app/root/project-that-generates-artifacts/-/artifacts

If the review app has been stopped by the time you're doing this:

1. retry the start-review-app-pipeline job to start it again
2. if you don't see the Artifacts link in the sidebar, enable the artifacts_management_page feature flag in the review app environment (see Enable a feature flag for my review app)

to run tests

1. bundle exec rspec spec/frontend/fixtures/job_artifacts.rb to generate the graphql fixture
2. yarn jest artifacts to run all artifacts jest tests

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.