Code Review Analytics: Replace legacy filtered search with Vue implementation

We're using the legacy filtered search bar (which is built in HAML and plain JS) on the Code Review Analytics page.

We should look into replacing the outdated search implementation with the gitlab/ui filtered search.

Implementation Plan:

• Introduce feature flags: !29580 (merged)
• Implement filtered search bar: !29669 (merged)
  • Create milestone token: !30610 (merged)
  • Create label token (!30706 (merged))
  • Implement Vuex store for filters: !30361 (merged)