Add metrics command / output to debug bundle

[davemay99]

This PR adds a metrics.json file to each interval captured by the nomad operator debug command. A new CLI sub-command nomad operator metrics and associated plumbing was added to support this feature, and also allow easier access for operators to gather metrics requested by support. Data is retrieved using the existing /v1/metrics API endpoint.

Future improvements will optionally collect metrics from each server/client node specified.

[davemay99]

I wasn't sure about how to handle updating the vendor directory. What is the preferred method to bring that up to date with my changes?

[drewbailey]

@davemay99 running make sync will take care of the vendor changes

[drewbailey]

Nice work!

I think I only have one comment, for the api operator Metrics method it would be nice to return something better than a string. For the command use case and operator debug where we are just writing it to a file this is fine, but for other API package users we probably want something easier to work with.

The issue here is that the actual endpoint returns either a MetricsSummary, or a prometheus format depending on the format query param. We could have two api/operator Metrics methods which set the query format for the user, or we could return []byte and let the callers parse the json themselves.

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[davemay99]

The issue here is that the actual endpoint returns either a MetricsSummary, or a prometheus format depending on the format query param. We could have two api/operator Metrics methods which set the query format for the user, or we could return []byte and let the callers parse the json themselves.

I originally had the []byte conversion to string in the operator debug code, but thought it would save a step by doing the conversion at the source. I switched back to []byte to leave it open for future expansion.

[drewbailey]

LGTM!

[drewbailey]

@davemay99 forgot, will need a follow up pr or issue to track adding the CLI docs to the io site

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