Plugin health for controllers should show "Node Only" in the UI only when both
conditions are true: controllers are not required, and no controllers have
registered themselves (0 expected controllers). This accounts for "monolith"
plugins which might register as both controllers and nodes but not necessarily
have `ControllerRequired = true` because they don't implement the Controller
RPC endpoints we need (this requirement was added in #7844)
This changeset includes the following fixes:
* Update the Plugins tab of the UI so that monolith plugins don't show "Node
Only" once they've registered.
* Add the missing "Node Only" logic to the Volumes tab of the UI.
aa7c77d324