Add agent command for reporting metrics

[stympy]

I wanted to report metrics from our servers to Insights without using Vector, so I had Claude help me add an agent command that does that. :)

In the future we can have this command also spin up a proxy for relaying notices and events.

Metrics look like this in Insights:

[joshuap]

I noticed that TestAgentCommand only actually runs the agentCommand in the "requires API key" test, but it's just testing reportMetrics directly otherwise. The name of the test implies that it's testing reporting metrics through the agent command. 🤷

[stympy]

@rabidpraxis from a querying/charting standpoint, would it be better to report an event per metric rather than having all the metrics combined in one event? If so, would it be better to report an event per disk vs. having all disks in an array?

[rabidpraxis]

It should be fine to have all the metrics in the same event.

The array of disks start to get tricky as it can be challenging to filter on a single disk (by name for example) or to do something like get the max bytes of all the disks. Having each one be an event would make it much simpler to work with.