Add metrics endpoint with http metrics using Prometheus client lib

[mmianl]

Fixes #408

Requirements

Enable basic Prometheus compatible instrumentation capabilities

Description of the Change

Add metrics endpoint with basic http and go related metrics when running api serve which can be enabled or disabled by a switch in the config file (= enableMetricsEndpoint)

Checklist

• unit-test added (if change is algorithm)
• functional test added/updated (if change is functional)
• man page updated (if applicable)
• bash completion updated (if applicable)
• documentation updated
• author name in AUTHORS

[mmianl]

Hello there,
what do you think of this change? The metrics endpoint can now be enabled or disabled by config file.

[randombenj]

Hi @mmianl
Thanks a lot for the changes! Do you think you could add some simple tests to verify the functionality?

[mmianl]

Hi @randombenj
Yes, I can certainly take a look at functional tests, I don't think that unit tests make a lot of sense, what do you reckon?

[randombenj]

@mmianl Yeah that's also what I would propose, thanks!

[mmianl]

Hello @randombenj,
Do you think this can be merged now?

[randombenj]

LGTM

[randombenj]

Cool change, thanks!