harmonytask feature: find clean-up work when underutilized.

[snadrus]

A helper for correct handling of different syncs for potential new harmony tasks. This will allow tasks to be created on demand of available resources so that both batching and non-batching processes can consume from the same inflow.

Proposed Changes

Pipelines' first steps can implement TaskDefinition.IAmBored to scrounge up more work when they have the capacity to work it.
Mid-pipeline stages can look at later failed stages for advanced recovery.

Additional Info

Checklist

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[jennijuju]

please have better PR titles as lotus release notes are generated off them

[snadrus]

@magik6k

[magik6k]

Looks good, and I'm going to need that soon for some automatic GC processes