* Allow user to specify `artifacts:expose_as` in CI config
* Save :has_exposed_artifacts in job metadata for queries
* Find exposed artifacts in build metadata model
* Expose API endpoint for frontend to fetch data

Fix unlrelated controller specs

Use default has_exposed_artifacts NULL

Avoid using a background migration to change NULL
to false. It's not needed.

Feedback from review

* add links to issue for follow up refactoring
* preload job artifacts and metadata associations
* merge DisallowedRegexInArrayValidator into existing
ArrayOfStringsValidator
* other minor changes

Rename params to match frontend code

Feedback from review

Feedback from review