Add onWorkflowPublish event to TraceObserverV2

[robsyme]

Summary

Adds a new onWorkflowPublish event to TraceObserverV2 that fires for each value as it is published to a workflow output.

This addresses the request in #6680 for richer context during file publishing. The new event provides:

• name - the workflow output name (e.g., "alignedBams")
• value - the complete channel value being published (which may contain files alongside metadata like sample IDs)

Event timeline

Channel value 1 arrives → onWorkflowPublish ← NEW (fires per value)
→ onFilePublish (for each file)
Channel value 2 arrives → onWorkflowPublish ← NEW
→ onFilePublish (for each file)
...
All values complete → onWorkflowOutput (fires once at end)

Unlike onWorkflowOutput which fires after all values have been published, onWorkflowPublish fires in real-time as each value flows through, giving

1. access to the published values as items in a channel, preserving the channel structure (items in the same channel element are together), and
2. observers immediate access to the complete channel emission.

Test plan

• Existing OutputDslTest tests updated to verify notifyWorkflowPublish is called
• Smoke tests pass

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[bentsherman]

I think this is the right idea

I'm wondering whether we should only fire this event for queue channels and not value channels. Since a value channel is just a single value, the onWorkflowPublish and onWorkflowOutput are identical, and if you use both events, you'll have to be careful to not do something twice. But depending on the use case, it may not matter

[pditommaso]

as a developer I wonder what's the difference of onWorkflowOutput vs onWorkflowPublish vs onFilePublish.

At least there should be a very detailed docs and javadoc describing what event is meant for and when to use it

Comments were addressed

[bentsherman]

I updated the java docs to be more comprehensive. I will follow up with a guide in the docs for how to use the trace observer

[robsyme]

Amazing. Thanks team ❤️ 🙏