Add http_pingpong

[mrceyhun]

It is useful to expose metrics behind authentication service, like cherrypy. Since localhost is exempted from authentication, http_pingpong can safely return results of service behind authentication.

Example scenario:

• We would like to get metrics of http://IP:8270/crabserver/metrics
• Run http_pingpong in same pod and provide another internal port to it, i.e.: default 17000
• Provide -uri parameter as http://localhost:8270/crabserver/metrics, -port parameter as 17000, -endpoint as /metrics:

go run http_pingpong.go -port ":17000" -endpoint "/metrics" -uri http://localhost:8270/crabserver/metrics

Now, we can reach crabserver/metrics response via curl http://IP:17000/metrics. Of course, in prod prebuilt executable will be used.

fyi @mapellidario @novicecpp , what do you think?

[mapellidario]

Sorry for the delay, I noticed the notification only now. It looks perfect to me, thank you veeery much! :)