Make prometheus metrics follow naming conventions

[petethepig]

Link to naming conventions: https://prometheus.io/docs/practices/naming/

Minimally we should do things like:

• add pyroscope_ prefix
• add proper suffixes, like _total or _bytes
• add tags where appropriate, e.g for badger metrics we should have trees and segments be tags, not parts of the name

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This would also be a good time to get rid of metrics package I think.

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After we update the names we should also update these dashboards:

• the one in ./benchmark
• the one in ./examples/grafana-integration
• the one on grafana website

[eh-am]

BTW

would be nice to add this prometheus metrics linter
https://github.com/yeya24/promlinter

it can be integrated with golangci-lint (yeah I know we are using revive, although it can be added to golangci-lint, see https://github.com/mgechev/revive#golangci-lint)

but anyway, to get the linter working it seems we would need to change/remove the metrics package, since the linter seems to expect a certain format (https://github.com/yeya24/promlinter/blob/master/promlinter.go#L191), plus having greppable metric names is always a good idea :)

[petethepig]

@eh-am this is a great idea, I think we should remove metrics package and then we can add the linter

[petethepig]

Closing because this was implemented a while ago