VACMS-9885 site previewer

[tjheffner]

Description

Closes #9885. Closes #9891.

This PR creates a feature flag for next preview, some next entity types to enable preview, and refactors the existing preview button logic from va_gov_backend.module to an Event Subscriber inside of va_gov_preview.

Please note: the vets-website assets are not yet correctly symlinked in place for next-build on CMS tugboat (will be a separate PR), so preview pages generated by next-build may take a few seconds to load and appear missing those vets-website-based portions. This will be fixed in a following PR.

Testing done

Enabled the feature flag and then tested a combination of nodes to ensure that next preview worked when enabled and that existing preview logic remained unchanged:

Next preview:
Story:
https://va-gov-cms.ddev.site/butler-health-care/stories/this-suicide-prevention-month-the-butler-va-offers-veterans-support

Story (draft revision):
https://va-gov-cms.ddev.site/node/61531/latest

Existing preview:
VAMC detail page:
https://va-gov-cms.ddev.site/southern-nevada-health-care/work-with-us/internships-and-fellowships/nurse-practitioner-residency

No preview (excluded type):
Events list:
https://va-gov-cms.ddev.site/northport-health-care/events

QA steps

What needs to be checked to prove this works?
What needs to be checked to prove it didn't break any related things?
What variations of circumstances (users, actions, values) need to be checked?

• Check a story node, note that the existing preview button is unchanged, using the current preview link format:
  https://pr16138-d6emmi3dibioikbr8bbq6bgzw8z1tgfl.ci.cms.va.gov/minneapolis-health-care/stories/its-never-too-late-to-quit-smoking-and-start-breathing-easier

• Check a story listing node, note that there is no preview button:
  https://pr16138-d6emmi3dibioikbr8bbq6bgzw8z1tgfl.ci.cms.va.gov/chicago-health-care/stories

• Enable the FEATURE_NEXT_STORY_PREVIEW feature flag at: https://pr16138-d6emmi3dibioikbr8bbq6bgzw8z1tgfl.ci.cms.va.gov/admin/config/system/feature_toggle

• Return to a story node, note that the preview button now points to the next-build server:
  https://pr16138-d6emmi3dibioikbr8bbq6bgzw8z1tgfl.ci.cms.va.gov/minneapolis-health-care/stories/its-never-too-late-to-quit-smoking-and-start-breathing-easier

• Return to a story listing node, note that a preview button now exists and points to the next-build server:
  https://pr16138-d6emmi3dibioikbr8bbq6bgzw8z1tgfl.ci.cms.va.gov/chicago-health-care/stories

• Check an Event List node, note that there is no preview button: https://pr16138-d6emmi3dibioikbr8bbq6bgzw8z1tgfl.ci.cms.va.gov/northport-health-care/events

• Check a VAMC detail page, note that the preview button is generated with existing preview link format (not pointing at next-build):
  https://pr16138-d6emmi3dibioikbr8bbq6bgzw8z1tgfl.ci.cms.va.gov/eastern-colorado-health-care/work-with-us/internships-and-fellowships/orthopaedic-physical-therapy-residency-program

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

[tjheffner]

noting this plugin isn't actually used by the PreviewEventSubscriber, but it does provide an drastically-less-experience-altering alternative to the full-page iframe takeover of a node view page that the default plugin provided by drupal/next does.

next.settings.yml has been configured to use it by default, but it should realistically never render to a page in this manner, because we render buttons that handle both versions of preview ourselves in the PreviewEventSubscriber.

[ndouglas]

Verified QA steps 🙂

[timcosgrove]

This is approved; however, we are making a call to hold merging this until after the Thanksgiving holiday.