[Merge Requests] Add a visual toggle for including archived projects in search results

Proposal

For the merge_requests scope using feature flag: search_merge_requests_hide_archived_projects (gated to user actor)

Add a filter for including archived projects which sends include_archived=true to the backend.

This requires adding a toggle to include archived project results on all project-related search results

Should be done for basic and advanced searches

Note: The toggle should show up for Group and Global searches. Project scoped searches will return results whether the project is archived or not