chore(llmobs): add telemetry to track llmobs usage

[rarguelloF]

What does this PR do?

Track usage of core llmobs apis.

Additionally, it renames the llmobs benchmark BenchmarkStartSpan to BenchmarkLLMObsStartSpan to not clash with the existing apm benchmark, and adds it to the .gitlab-ci.yml config.

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.
• New code is free of linting errors. You can check this by running ./scripts/lint.sh locally.
• 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.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-31 15:20:38

Comparing candidate commit 05de3d7 in PR branch rarguelloF/llmobs-telemetry with baseline commit 5ef8e9b in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.

[darccio]

LGTM

[datadog-datadog-prod-us1]

⚠️ Tests

⚠️ Warnings

❄️ 1 New flaky test detected

TestMultipleSpanIntegrationTags from github.com/DataDog/dd-trace-go/v2/ddtrace/tracer (Datadog)

Failed

=== RUN   TestMultipleSpanIntegrationTags
    metrics_test.go:219: 
        	Error Trace:	/home/runner/work/dd-trace-go/dd-trace-go/ddtrace/tracer/metrics_test.go:219
        	Error:      	Condition never satisfied
        	Test:       	TestMultipleSpanIntegrationTags
panic: not implemented

goroutine 1327 [running]:
...

ℹ️ Info

🧪 All tests passed

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 05de3d7 | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[darccio]

/merge

[dd-devflow-routing-codex]

View all feedbacks in Devflow UI.

2025-10-31 15:09:48 UTC ℹ️ Start processing command /merge

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2025-10-31 15:09:58 UTC ℹ️ MergeQueue: waiting for PR to be ready

This pull request is not mergeable according to GitHub. Common reasons include pending required checks, missing approvals, or merge conflicts — but it could also be blocked by other repository rules or settings.
It will be added to the queue as soon as checks pass and/or get approvals.
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2025-10-31 15:56:24 UTC ℹ️ MergeQueue: merge request added to the queue

The expected merge time in main is approximately 18m (p90).

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2025-10-31 16:11:19 UTC ℹ️ MergeQueue: This merge request was merged