Allow external workers.

[Foxcapades]

Presently the compute platform only supports internal threadpools as job queue consumers. The platform should also support submitting jobs to queues that are read by external workers.

[Foxcapades]

This is a requirement for updating multiblast to use the new platform.

[Foxcapades]

This would require abandoning the metrics for queue size and queue wait time. Instead of doing this, perhaps the worker threads could be making the request out to the external system to trigger the jobs?

[Foxcapades]

Not necessary.