feat: Collector Metric Exporter[2/x] Create CollectorMetricExporterBase

[davidwitten]

Summary

This PR addresses Issue #1109.

Currently, the Collector Exporter only sends traces to the collector. In Python, Java, and Go, for example, metric exporting already exists for the collector. This PR adds that feature. I created two versions, one for Node and the other for browser. The node version uses gRPC, and the browser uses Beacon or XHR. It's up to date with all previous collector exporter commits.

What this PR does

This is the 2nd part of this long PR.

This PR creates CollectorMetricExporterBase, modeled off CollectorTraceExporterBase. I also create unit tests and add two mock metrics to test with, a mock counter and a mock observer. The base class does nothing, so this won't break anything.

Next Steps

The next diffs will be as follows

1. Add transform functions and tests
2. E2E Metric exporter for Browser with tests
3. E2E Metric exporter for Node with tests

[codecov]

Codecov Report

Merging #1258 into master will increase coverage by 0.01%.
The diff coverage is 91.48%.

@@            Coverage Diff             @@
##           master    #1258      +/-   ##
==========================================
+ Coverage   93.01%   93.03%   +0.01%     
==========================================
  Files         131      132       +1     
  Lines        3696     3735      +39     
  Branches      747      755       +8     
==========================================
+ Hits         3438     3475      +37     
- Misses        258      260       +2     

Impacted Files	Coverage Δ
...ages/opentelemetry-exporter-collector/src/types.ts	100.00% <ø> (ø)
...orter-collector/src/CollectorMetricExporterBase.ts	89.74% <89.74%> (ø)
...porter-collector/src/CollectorTraceExporterBase.ts	94.87% <100.00%> (+5.12%)	⬆️

[davidwitten]

This PR: #1254 reverted my proto change, so I'm doing it again.

[dyladan]

Looks good thanks for the contribution

[naseemkullah]

nit: hostname is one word, other than that and apparent lack of code coverage lgtm

[davidwitten]

@naseemkullah Actually, I realized that this.hostname is also set in CollectorTraceExporterBase and is never used. Is it okay to just remove it from both?

[naseemkullah]

@naseemkullah Actually, I realized that this.hostname is also set in CollectorTraceExporterBase and is never used. Is it okay to just remove it from both?

At a quick glance, imho, we can remove hostname but we should add host and port, which should be used with Node, whereas url with browser, since for reasons beyond my understanding they must be configured differently. @open-telemetry/javascript-maintainers please advise.

edit: It's just weird in Node's case that the value of url is not a url

[naseemkullah]

All that to say I'm ok with removing hostname and (eventually adding host and port, probably not in this PR, if Node cannot be configured via url with a url).

[davidwitten]

Thanks @naseemkullah! For now, I just changed hostName to hostname and added more unit tests. I'll make another PR to remove it and replace it with host/port.

[obecny]

As this i based already on CollectorTraceExporter can you please align name hostName in both places so it will be also hostname ? ignore I see you already did

[obecny]

lgtm
Nit: please rename CollectorExporter in tests into CollectorTraceExporter