contrib/internal/httptrace: add inferred span identification tag

[zarirhamza]

What does this PR do?

Adds _dd.inferred_span tag to ID inferred span tags

Motivation

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/inferred_span_tag
Commit report: 9541c59
Test service: dd-trace-go

✅ 0 Failed, 5235 Passed, 73 Skipped, 1m 48.73s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-13 18:21:43

Comparing candidate commit f18cb33 in PR branch zarir/inferred_span_tag with baseline commit 9eb2e61 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 62 metrics, 0 unstable metrics.

[hannahkm]

Looks good! Failing orchestrion test seems to be unrelated; try rerunning to see if it passes.

Also, please cherry pick the PR to the v2-dev branch! Or DM me if you'd like one of us to do it instead.