Docs/Tests: documentation and e2e tests for Datadog tracing

[Hartigan]

Hi

This PR introduce documentation and end-to-end tests for Datadog tracing which added in #4298

End-to-end test implemented via Grafana Alloy, where Alloy acts as adapter from Datadog agent interface into OpenTelemetry format.

Thanks

[Hartigan]

@zirain , may you take a look?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.84%. Comparing base (5a1c065) to head (149e937).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4480      +/-   ##
==========================================
+ Coverage   65.80%   65.84%   +0.04%     
==========================================
  Files         203      203              
  Lines       30696    30699       +3     
==========================================
+ Hits        20200    20215      +15     
+ Misses       9341     9333       -8     
+ Partials     1155     1151       -4     

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[zirain]

Generally LGTM, thanks for adding this.

[zirain]

/retest

[zirain]

Now the pipeline looks like [Envoy] -> [Alloy] -> [OTel-collecotr] -> [Tempo], right?
Does OTel-collector[-contrib] could play as Datadog backend?

[Hartigan]

@zirain yes.
Looks like Opentelemetry collector has Datadog receiver support. I may try rewrite test without Alloy.

[Hartigan]

Now test uses only opentelemetry-collector without Alloy. Also, I updated opentelemetry-collector to 0.108.0

[Hartigan]

@zirain should I mention somebody for additional review or approval?

[arkodg]

thanks for also adding docs and e2e @Hartigan !