Adds namespace support to the UI:
1. Namespace CRUD/management
2. Show Namespace in relevant areas (intentions, upstreams)
3. Main navigation bar improvements
4. Logic/integration to interact with a new `internal/acl/authorize` endpoint
1. Rebuild the heathchecked-resource component now we can copy and paste
2. As the above rebuild came with new icons, we also swapped out 'most'
of the other areas where we were using these new icons, plus any icons
that were effected by the new icon placeholders
3. Begin to remove more and more of the project specific icons (now
replaced by the shared ones)