Trim sisiphys -> gaia kafka messages

[1fish2]

Trim sisiphys -> gaia kafka msgs down to:

• step-start
• step-complete
  • Compute next tasks to run and workflow complete/stalled/continues once per task completion, not per file data-complete.
  • This will save time, esp. at scale, and make STEP COMPLETE appear in the log before WORKFLOW COMPLETE.
• step-error -- puts the task in state :error
• task-error -- puts the task in state :exception
  • What's the difference? Merge this with step-error or rename it to step-exception.
  • Does Gaia need to distinguish step-terminated and step-timeout?

Check that Gaia and Sisyphus match up in all the Kafka messages, including when some part of a task fails.