Added Monitor.

This adds 'monitor', the third way to use Strata.

Unlike a Client or Service, and Monitor behaves like a Service in that it listens for messages, but it does so on it's own Consumer Group, and simply emits a message event for every message it monitors. That's it. It cannot send or receive message; for those you would use a Client or Service respectively.

These changes do introduce a breaking change to Client, to bring it's configuration in line with the rest of Strata. Users of Client will need to wrap the redis config in an object with the key redis. (i.e. { redis: { ...oldConfig } }.)

This is required by tools/strata-queue-monitor.