Metrics - Workflow setup

[Vafilor]

We want to record metrics automatically for a workflow.

Add an additional exit handler to the last nodes of a workflow to read the metrics file and send an API request to update the metrics.

One implementation idea is to check if the file exists in the shell, and if it does then use a CURL command to post it.

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[Vafilor]

This one is currently in discussion as it might be too problematic when there are multiple leaf nodes in the DAG. We don't want to create problems deciding which metrics to merge/override.