Frontend requires pinmanager to provide QoS information

[paulmillar]

A query to the namespace resources that requests that QoS be resolved (e.g., /api/v1/namespace/directory?qos=true) uses external components to build the QoS.

On a purely disk based dCache, pinmanager is an optional component. However, the directory listing with QoS will fail if pinmanager is not running.