Add Vue 3 rollout flag for requirements page

What does this MR do and why?

This MR adds the vue3_migrate_requirements flag and a vue3_migration.yml for the project requirements page entrypoint. This opts it into the Vue 3 migration with Option 1.

Entrypoints

• pages.projects.requirements_management.requirements

References

https://docs.gitlab.com/development/fe_guide/vue3_migration/#option-1-recommended-migrate-your-page-entrypoint-using-a-feature-flag-and-vue3_migrationyml

Screenshots or screen recordings

How to set up and validate locally

1. Enable the feature flag vue3_migrate_requirements flag
2. Head over to a projects requirements management page (eg. )
3. Open the console and confirm you see [gitlab] [V] Using Vue.js 3 (with @vue/compat) for RequirementsRootRoot and no errors

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.

Related to #608118 (closed)