Add an option to disable WorkManager processing

Defining Nuxeo node that schedules async works but doesn't process them is useful to separate load and scale.

On the WorkQueueDescriptor there is a flag to enable the queue and a flag to enable/disable the processing.

For instance to disable all async processing for a Nuxeo node we can do:

  <extension target="org.nuxeo.ecm.core.work.service" point="queues">
    <queue id="*" processing="false"/>
  </extension>

But you need to put the right requirements so the contribution is the last one, this is not always possible and it would be better to have an option in the configuration service for this.

This should work for both WorkManager implementation (default and stream).