Force CI schema URL to be absolute

What does this MR do?

Fix for #297252 (closed).

In order for workers loaded from data:// as the ones loaded by monaco, we use absolute URLs to fetch schema files, hence the location.origin reference. This prevents error: "Failed to execute 'fetch' on 'WorkerGlobalScope'"

Note: This change requires the flags ci_pipeline_editor_page and schema_config to be enabled.

Screenshots (strongly suggested)

This is hard to test on gdk, so I used a review app to check, I hope this is close enough to production:

https://gitlab-review-297252-ci-df264v.gitlab-review.app/root/my-ci-project/-/ci/editor

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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

Related to #297252 (closed)