RFR: bot: add metrics HTTP handler

[Erik Joelsson]

On Wed, 12 May 2021 17:56:36 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this patch that adds an HTTP handler for metrics to the bot runner. Typically listening on the `/metrics` path the handler will return metrics according to Prometheus text format.
> 
> Testing:
> - [x] Tested manually with a Prometheus instance on Linux x64
> 
> Thanks,
> Erik

Marked as reviewed by erikj (Reviewer).

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PR: https://git.openjdk.java.net/skara/pull/1152