Create stdout metrics exporter

[MadVikingGod]

closes #2805

This adds the first exporter back to the SDK. This changes the stdout metrics from a custom format, I think modeled after prometheus, to just json. We have not had any stability guarantees of the output format of the stdout exporter, as they are intended for development.

[codecov]

Codecov Report

Merging #3056 (961c66b) into new_sdk/main (8ac0588) will increase coverage by 1.9%.
The diff coverage is 85.8%.

@@              Coverage Diff               @@
##           new_sdk/main   #3056     +/-   ##
==============================================
+ Coverage          74.0%   76.0%   +1.9%     
==============================================
  Files               114     127     +13     
  Lines              7930    8895    +965     
==============================================
+ Hits               5874    6761    +887     
- Misses             1921    1981     +60     
- Partials            135     153     +18     

Impacted Files	Coverage Δ
attribute/value.go	88.9% <ø> (ø)
bridge/opentracing/util.go	100.0% <ø> (ø)
bridge/opentracing/wrapper.go	100.0% <ø> (ø)
exporters/jaeger/uploader.go	48.2% <0.0%> (-0.4%)	⬇️
exporters/stdout/stdouttrace/config.go	100.0% <ø> (ø)
handler.go	100.0% <ø> (ø)
internal/matchers/expectation.go	0.0% <0.0%> (ø)
metric/instrument/config.go	0.0% <0.0%> (ø)
metric/internal/global/instruments.go	54.3% <ø> (-3.0%)	⬇️
metric/noop.go	100.0% <ø> (ø)
... and 56 more

[MrAlias]

Hmm, I took the assignment of #2805 and have a working proof-of-concept that I was going to submit as a PR today after completing tests. It takes a slightly different approach to the encoding of data. It allows for a generic encoder to be passed and configured by the user, while still maintaining the original output format.

I'm bummed that we weren't able to prevent duplicate effort here. How would you like to proceed?

[MadVikingGod]

Sorry, I'll admit I didn't check the status of the issue and have just been working on this in downtime.

If you have a more flexible exporter, I'm totally ok taking that one over this.

[MrAlias]

Sorry, I'll admit I didn't check the status of the issue and have just been working on this in downtime.

If you have a more flexible exporter, I'm totally ok taking that one over this.

Let me get a draft up in the next hour or so for you to take a look at. It will not be complete in that it does not have a full test suite, but should be good enough to get the broad strokes. I'll let you decide how we want to progress from there.

[MrAlias]

Sorry, I'll admit I didn't check the status of the issue and have just been working on this in downtime.
If you have a more flexible exporter, I'm totally ok taking that one over this.

Let me get a draft up in the next hour or so for you to take a look at. It will not be complete in that it does not have a full test suite, but should be good enough to get the broad strokes. I'll let you decide how we want to progress from there.

#3057

[MadVikingGod]

Closing, #3057 is a better direction.