Implement Conversion Between OC and OTel Summary Metric

[JasonXZLiu]

Note: This PR is based off the Summary datapoint proto (that has not been merged upstream) in this PR.

Description:

This PR has two main parts:

• Implement the Summary datapoint proto in the OTel Collector. Changes were made to metrics_struct.go to create the generated Summary structs (using the make genproto and make genpdata commands).
• Add in the conversion between OpenCensus summary metrics and OTel Summary datapoints. This conversion directly adds compatibility for the Prometheus Summary metric in the PrometheusReceiver.

Link to tracking Issue: opentelemetry-specification/issues/1146 and opentelemetry-collector/issues/1638

A lot of the code in this PR is auto-generated from creating the structs and protos. The following files are were auto-generated:

• generated_metrics.go
• generated_metrics_test.go
• trace_config.pb.go
• metrics.pg.go

Testing:

• Updated unit tests in oc_to_metrics.go for conversion between OC summary metrics to OTel summary metrics
• Created end-to-end tests for the Summary metric in PrometheusReceiver

cc - @alolita

[codecov]

Codecov Report

Merging #2048 into master will increase coverage by 0.11%.
The diff coverage is 96.58%.

@@            Coverage Diff             @@
##           master    #2048      +/-   ##
==========================================
+ Coverage   92.04%   92.15%   +0.11%     
==========================================
  Files         278      278              
  Lines       16831    17120     +289     
==========================================
+ Hits        15492    15777     +285     
- Misses        921      923       +2     
- Partials      418      420       +2     

Impacted Files	Coverage Δ
translator/internaldata/metrics_to_oc.go	90.56% <86.95%> (-0.62%)	⬇️
translator/internaldata/oc_to_metrics.go	91.77% <88.23%> (-0.62%)	⬇️
consumer/pdata/generated_metrics.go	100.00% <100.00%> (ø)
consumer/pdata/metric.go	99.37% <100.00%> (+0.05%)	⬆️
internal/data/testdata/metric.go	100.00% <100.00%> (ø)
receiver/otlpreceiver/otlp.go	92.30% <0.00%> (+2.56%)	⬆️
translator/internaldata/resource_to_oc.go	94.52% <0.00%> (+5.47%)	⬆️

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[rakyll]

Leaving the data conversion related review to the approvers. I left some high level questions and suggestions.

[bogdandrutu]

This needs to wait for the proto change to be merged.

[bogdandrutu]

@tigrannajaryan do you suggest to not update now? This blocks some important feature for AWS.