Http and info metrics

[eh-am]

• tracking http metrics (request duration, size of response)
• added pyroscope_build_info to expose version as a metric, similar to https://www.robustperception.io/exposing-the-software-version-to-prometheus
• added latency/error rate/throughput (per endpoint) pane in the dashboard

[codecov]

Codecov Report

Merging #347 (80d736a) into main (c566451) will decrease coverage by 0.08%.
The diff coverage is 56.42%.

@@            Coverage Diff             @@
##             main     #347      +/-   ##
==========================================
- Coverage   54.40%   54.32%   -0.07%     
==========================================
  Files         102      102              
  Lines        4986     5013      +27     
==========================================
+ Hits         2712     2723      +11     
- Misses       2025     2041      +16     
  Partials      249      249              

Impacted Files	Coverage Δ
pkg/build/build.go	2.95% <0.00%> (-0.76%)	⬇️
pkg/cli/server.go	7.90% <0.00%> (ø)
pkg/util/debug/reporter.go	0.00% <0.00%> (ø)
pkg/server/controller.go	35.13% <100.00%> (+3.33%)	⬆️
pkg/server/http.go	100.00% <100.00%> (ø)

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[eh-am]

exposing the following fields

pyroscope_build_info{GOARCH="amd64",GOOS="linux",revision="fb579a0e",time="2021-08-24T15:01:13Z",use_embedded_assets="false",version="v0.0.37"} 1