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
Previously we were creating a fake event and amending the name of the
fake event, this meant that other `event.target` properties weren't
being passed through (in this instance `checked`) this changes the
approach to not use fake events, and allows you to overwrite the name
that the form uses for `handleEvent`