Expose endpoint to control streams

[morgsmccauley]

Coordinator requires a direct control point to the Block Streamer service so that it can control the state of the existing Streams.

An endpoint with the following capabilities should be exposed:

• Start an Block Stream
• Stop an Block Stream
• List existing Block Streams

As this is part of the new Block Streamer service, we don't need to implement a toggle like we are in Runner. The toggle exists at the system level by starting either this service, or Coordinator V1.