WIP: A11y testing

What does this MR do?

This MR is the beginning of a solution for #54806 (moved)

This is the direction I'm starting to go in for building specs that assert the creation of report artifacts. The idea is that we want to ensure that a config file written in a certain way results in particular artifacts being created and made available via internal API.

The scope of this can be kept small for now; simply asserting that given YAML config specifying a report artifact for performance called performance.json, a produced Ci::Build has something distinct about it from a build whose pipeline config does not specify that report.

The exist and not-exist case for one report type is built below. If you run them, you'll see the performance report artifact is not present in either case. I. know that it can be (in the second case with all the performance testing config), but I'm not sure of the best way to set up a Pipeline and Build where that's the case.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team