Proposal: create metrics from traces and agent based sampling

[Hartigan]

Hi

This fraft pull request introduce 2 features from datadog telemetry protocol:

1. Measurements - if _dd.measured flag present in span, datadog agent automatically creates metrics from this span.
2. Agent based sampling - by default ALL spans generated by dd-trace-agent exported to trace-agent. And agent decide export span or not to Datadog cloud service. This decision based on _sampling_priority_v1 flag and trace-agent configuration(ex. force to sample error spans).

Described flags, may be propagated or changed by ShouldSample interface

Current code not working, because decision about export trace or not created here

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Hartigan (a55ca71, ee83e24, 40e14c2, 884bfe4, 8c56f6f, 88e04f2, a5afbb8, f2a9fac, 46a6663, 859884f, 4664dfc, 2703323)
• ✅ login: cijothomas / name: Cijo Thomas (d21095d, f4a3737)

[cijothomas]

@Hartigan Could you clear the EasyCLA check before we can accept any contributions? You may want to consult your employer's legal team, if needed.

[Hartigan]

Hi @cijothomas

Should I change smth in this pull request(api or add custom implementation of ShouldSample)? Or write some tests for this?

[cijothomas]

Hi @cijothomas

Should I change smth in this pull request(api or add custom implementation of ShouldSample)? Or write some tests for this?

I am not an expert in this component, so can't give a specific suggestion. I hope there are DataDog experts or other owners of this component who can help.

[TommyCpp]

Some unit tests are always welcome!

[codecov]

Codecov Report

Attention: Patch coverage is 84.42623% with 19 lines in your changes are missing coverage. Please review.

Project coverage is 52.4%. Comparing base (e23abe4) to head (f4a3737).

Files	Patch %	Lines
opentelemetry-datadog/src/lib.rs	83.9%	17 Missing ⚠️
opentelemetry-datadog/src/exporter/model/v05.rs	87.5%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main     #17     +/-   ##
=======================================
+ Coverage   51.7%   52.4%   +0.6%     
=======================================
  Files         37      37             
  Lines       4918    5026    +108     
=======================================
+ Hits        2544    2635     +91     
- Misses      2374    2391     +17     

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[hdost]

Thank you for the contribution, also make sure to add a comment into the CHANGELOG.md.

[cijothomas]

@Hartigan Could you resolve conflicts? Thanks!

[cijothomas]

Not an expert in this particular component, so will wait another day before merge to see if anyone else can help with additional reviews.

[cijothomas]

@Hartigan could you resolve conflicts, so we can merge?