contrib/internal/httptrace: add telemetry for inferred spans

[zarirhamza]

What does this PR do?

Adds telemetry for inferred span tracking only if the env var DD_TRACE_INFERRED_PROXY_SERVICES_ENABLED is set to true

Motivation

Track usage of new inferred proxy spans

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.
• For internal contributors, a matching PR should be created to the v2-dev branch and reviewed by @DataDog/apm-go.

Unsure? Have a question? Request a review!

[datadog-datadog-prod-us1]

Datadog Report

Branch report: zarir/add-telemetry-inferred-spans
Commit report: 67114d2
Test service: dd-trace-go

✅ 0 Failed, 5207 Passed, 72 Skipped, 2m 20.08s Total Time

[rarguelloF]

I don't think you want to send this telemetry every time there is an http request. I think this makes more sense to be tracked when the configuration is initialized, which would be in the newConfig function from this package.

[zarirhamza]

Fixed by wrapping it with sync.Once. Cannot move to config file because all those variables are called pre tracer and telemetry client initialization

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-27 18:01:15

Comparing candidate commit ae023f4 in PR branch zarir/add-telemetry-inferred-spans with baseline commit ef2e4e2 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 59 metrics, 0 unstable metrics.

[kakkoyun]

LGTM.