Prometheus metric endpoint and Opentelemetry stats

[manute]

Issue #171

Description of changes:

• Adds the possibility of running one http server, with a /metrics handler for prometheus, behind a configuration flag.
• Leverage this PR to add Opentelemetry stats , useful for later add distrubuted tracing or export the metrics to other provider.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #172 into master will decrease coverage by 0.06%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master     #172      +/-   ##
==========================================
- Coverage   81.37%   81.30%   -0.07%     
==========================================
  Files           8        8              
  Lines         757      765       +8     
==========================================
+ Hits          616      622       +6     
- Misses        126      128       +2     
  Partials       15       15              

Impacted Files	Coverage Δ
pkg/node/node.go	59.68% <0.00%> (-0.39%)	⬇️
pkg/config/config.go	100.00% <100.00%> (ø)

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[bwagner5]

Great work on this! I just had a few comments in-line.

[bwagner5]

NOTE: Reviewed licenses 👍

TODO: add to to thirdparty licenses file.

✅ github.com/modern-go/concurrent                      Apache License 2.0
✅ golang.org/x/oauth2                                  BSD 3-Clause "New" or "Revised" License
✅ go.opentelemetry.io/otel/exporters/metric/prometheus Apache License 2.0
✅ google.golang.org/grpc                               Apache License 2.0
✅ k8s.io/apimachinery                                  Apache License 2.0
✅ github.com/googleapis/gnostic                        Apache License 2.0
✅ golang.org/x/time                                    BSD 3-Clause "New" or "Revised" License
✅ go.opentelemetry.io/otel                             Apache License 2.0
✅ github.com/prometheus/common                         Apache License 2.0
✅ github.com/modern-go/reflect2                        Apache License 2.0
✅ github.com/gogo/protobuf                             BSD 3-Clause "New" or "Revised" License
✅ github.com/prometheus/client_golang                  Apache License 2.0
✅ github.com/cespare/xxhash                            MIT License
✅ github.com/beorn7/perks                              MIT License
✅ golang.org/x/crypto                                  BSD 3-Clause "New" or "Revised" License
✅ github.com/google/gofuzz                             Apache License 2.0
✅ github.com/golang/protobuf                           BSD 3-Clause "New" or "Revised" License
✅ go.opentelemetry.io/contrib/instrumentation/runtime  Apache License 2.0
✅ golang.org/x/text                                    BSD 3-Clause "New" or "Revised" License
✅ github.com/prometheus/procfs                         Apache License 2.0
✅ k8s.io/client-go                                     Apache License 2.0
✅ k8s.io/kubectl                                       Apache License 2.0
✅ github.com/json-iterator/go                          MIT License
✅ github.com/prometheus/client_model                   Apache License 2.0
✅ k8s.io/api                                           Apache License 2.0
✅ golang.org/x/sys                                     BSD 3-Clause "New" or "Revised" License
✅ k8s.io/klog                                          Apache License 2.0
✅ github.com/rs/zerolog                                MIT License
✅ golang.org/x/net                                     BSD 3-Clause "New" or "Revised" License
✅ github.com/davecgh/go-spew                           ISC License
✅ gopkg.in/inf.v0                                      BSD 3-Clause "New" or "Revised" License
✅ github.com/DataDog/sketches-go                       Apache License 2.0
✅ k8s.io/utils                                         Apache License 2.0
✅ github.com/matttproud/golang_protobuf_extensions     Apache License 2.0
✅ sigs.k8s.io/yaml                                     MIT License
✅ k8s.io/kube-openapi                                  Apache License 2.0
✅ gopkg.in/yaml.v2                                     Apache License 2.0

[manute]

@bwagner5 I think I've addressed all of the requested changes.
It would be nice to have some help in the Travis build as I don't understand why it's failing.

[bwagner5]

@manute I've reviewed the changes you made, everything looks good to me. The intermittent failures on the tests is a known issue from a recently merged PR. I'll be looking into the tests to stabilize them soon.

Thanks for this contribution!

[bwagner5]

nice work! thanks!