Rollout Vue 3 migration for project wiki endpoints with feature flag

What does this MR do and why?

This MR introduces the vue3_migrate_wiki feature flag, allowing the Vue 3 rollout on wiki endpoints.

References

Issue URL: #608112 (closed)

Feature flag rollout URL: #627110

Screenshots or screen recordings

No UI changes

How to set up and validate locally

1. Make sure your GDK is configured to use vue 3: https://docs.gitlab.com/development/fe_guide/vue3_migration/#set-up-gdk-to-use-vue-3-vuecompat
2. open rails c and run Feature.enable(:vue3_migrate_wiki)
3. If not done yet, open or create a wiki (Plan > Wiki) at gitlab-org/gitlab-test with a page named "Home" that has the path home. You may use any other project or path, but will need to adjust the URLs below.
4. verify the following endpoints work and behave the same as on master:

• pages.projects.wikis.show: https://gdk.test:3443/gitlab-org/gitlab-test/-/wikis/home
• pages.projects.wikis.pages: https://gdk.test:3443/gitlab-org/gitlab-test/-/wikis/pages
• pages.projects.wikis.history: https://gdk.test:3443/gitlab-org/gitlab-test/-/wikis/home/history
• pages.projects.wikis.diff: https://gdk.test:3443/gitlab-org/gitlab-test/-/wikis/home/diff

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.