chore(runtime metrics): fix telemetry reporting [backport 3.1]

[github-actions]

Backport 7c26395 from #12515 to 3.1.

Currently runtime metrics configurations are queued every time a process forks and when a process shutdowns down (via forksafe and atexit hooks). This behavior is unique to runtime metrics and results in runtime_metrics being reported as disabled in the final telemetry event (sent when an application shuts down). This quirk can lead to incorrect analysis.

This PR ensures:

• The origin of runtime metrics is reported as code when runtime metrics is enabled via the public interface (ddtrace.runtime_metrics)
• The origin of runtime metrics configuration is reported as env_var/default when runtime metrics is enabled/disabled via import auto / ddtrace-run.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: backport-12515-to-3.1
Commit report: a703a13
Test service: dd-trace-py

✅ 0 Failed, 43 Passed, 460 Skipped, 1m 2.47s Total duration (9m 59.5s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-25 23:50:14

Comparing candidate commit a703a13 in PR branch backport-12515-to-3.1 with baseline commit cf224f4 in branch 3.1.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 386 metrics, 2 unstable metrics.