Implement streaming logs

[Matthew Vaughn]

One Abaco tenant rolled their own immediate-term logging system within their Docker images so that events could be captured from inside the execution into an ELK stack instance in real time, rather than waiting for the execution to complete. This has become important for monitoring and debugging complex, long-running, or highly stateful actors, and added sophisticated search and analytics to the logs as well. But, it seems a shame to replicate the Abaco logging functionality. This is not a very concrete proposal, but it would be interesting to explore if this function could be pushed down to the service level.