Warn user if test report generated with legacy requirement IID

frontend part of #388525 / #382141 (closed). Context in #382141 (comment 1171860767).

Users should be warned if their gitlab-ci.yml file contains legacy requirement IIDs.

• A ⚠ with text or similar, at test report view
• A popover to explain what that means, with links to docs
• Perhaps something at the repo level?

We'll probably also need documentation to explain it fully so users can take the necessary steps to update their gitlab-ci.yml and anywhere else they use legacy requirement IIDs.