Remove or Re-enable Global Search

### Current Behavior:
Dependency-Track contained a global search facility in versions up to and including 3.7.1. It "disappeared" when 3.8.0 was released with v1.0.0 of the frontend.

The backend logic is still present in the API server for this, and search indexes are still regularly updated.

### Proposed Behavior:
Re-enable the global search... use case is "Convenience feature to quickly find stuff without having to navigate to specific pages".

OR: remove the global search functionality from the API server.

Note that issue https://github.com/DependencyTrack/dependency-track/issues/645 describes some usability issues with the global search.