OpenAPI UI Hook to Event Subscriber

[alexfinnarn]

Description

Closes #16456 by moving a library attachment via a hook to an event subscriber.

Testing done

Manually tested that "/admin/config/services/openapi" only has one JSON schema listed to explore and Swagger UI still works.

Screenshots

QA steps

1. Log into to the CMS as a user who can get to "/admin/config/services/openapi".
2. Make sure only "VA.gov JSON:API" is listed under the Module column. JS hides two other options after the page loads that you'll probably see flicker while being removed.
3. Click "Explore with Swagger UI" and see that it still loads.

Definition of Done

• Documentation has been updated, if applicable.
• Tests have been added if necessary.
• Automated tests have passed.
• Code Quality Tests have passed.
• Acceptance Criteria in related issue are met.
• Manual Code Review Approved.
• If there are field changes, front end output has been thoroughly checked.

Select Team for PR review

• CMS Team
• Public websites
• Facilities
• User support
• Accelerated Publishing

[github-actions]

GitHub Workflows (.github/workflows/*.yml)

Have you...

• pinned all affected GitHub Actions at a specific commit by SHA?
• reviewed the source code of the action at the commit you are pinning?
• confirmed that no GitHub security measures are being bypassed?
• checked for any injection of user content into protected contexts?
• reviewed Security hardening for GitHub Actions?
• reviewed GitHub Workflows?

[tjheffner]

I had to clear caches for the swagger page to load correctly (complained about a missing schema prior), but otherwise this works well. Nice work on the event subscriber!