Add event subscriber to include situation updates for full banner width alerts

[alexfinnarn]

Description

closes #16781

Testing done

Manually tested as well as added/updated integration tests.

Screenshots

example output at "api/v1/banner-alerts".

QA steps

1. Edit a "full_width_banner_alert" node
   • Add two situation updates to that node
   • Figure out which path it loads on via the associated VAMC systems
2. Add a "banner" node that loads at the same path as the "full_width_banner_alert" node you just edited.
3. Add a "promo_banner" node that loads at the same path as the "full_width_banner_alert" node you just edited.
4. Go to /api/v1/banner-alerts?path=/your-path
   • Confirm that the "banner" data loads correctly
   • Confirm that the "promo_banner" data loads correctly
   • Confirm that the "full_width_banner_alert" data loads correctly and includes "field_situation_updates" paragraph data either in the "attributes" or "includes" section of the response.
5. Try not adding a path, /api/v1/banner-alerts, and confirm the response is error: "No path provided.".
6. Try a path that shouldn't return any data /api/v1/banner-alerts?path=/does-not-exist and confirm that no data is returned. Make sure to check if a promo/banner is set to * and shows on all paths. This might confuse your test since that banner will show even on paths Drupal thinks are 404s...and maybe this should be updated, but it wasn't in the scope of this ticket.

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?