Worker: add an option to not send run:log events

[josephjclark]

Run logs are noisy and pressure the websocket and lightning db. It might be useful in some cases to switch them off - if only to compare performance.

A short term solution would be to use an option to disable logs entirely

Another would be to not stream logs - just send all the logs together at the end of a step (or run?). So they do get sent, just not in real-time