Collect Holochain metrics from target nodes

[ThetaSinner]

When we run TryCP-based scenarios, we are running one control node and connecting to several targets that have TryCP and Holochain on them. We collect custom and host metrics from the control node but we don't yet collect any metrics from Holochain on the target nodes.

Depends on: #111

We could solve this in two ways

• Modify Holochain to integrate with Telegraf, and have TryCP launch Holochain with it configured to write metrics to file. At the end of the scenario we could have TryCP run Telegraf to push metrics to InfluxDB
• Investigate a tool that could run Wind Tunnel scenarios the way that they were originally designed to run. That is, without TryCP. Then figure out how to integrate Telegraf with that tool.

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• Holochain would need to know to push the run_id as a tag with each record
• How much work would it be to support both collecting metrics in real time and after the run?

[ThetaSinner]

I suggest that we do #111 before this, then we can decide which option we're going with and can add some AC for this issue.