fix(tracing): only apply rate limits to tracer sampled spans

[mabdinur]

Aligns the implementation of DD_TRACE_RATE_LIMIT with the java, dotnet and nodejs tracers: https://docs.datadoghq.com/tracing/trace_collection/library_config/java/#configuration-options.

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

[github-actions]

CODEOWNERS have been resolved as:

releasenotes/notes/only-rate-limit-on-sampling-rules-6f807defa7d0f5f1.yaml  @DataDog/apm-python
ddtrace/internal/rate_limiter.py                                        @DataDog/apm-core-python
ddtrace/sampler.py                                                      @DataDog/apm-sdk-api-python
docs/configuration.rst                                                  @DataDog/python-guild

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-09-23 20:38:51

Comparing candidate commit 8024426 in PR branch munir/only-rate-limit-on-sampling-rules with baseline commit 5546c23 in branch main.

Found 5 performance improvements and 0 performance regressions! Performance is the same for 351 metrics, 48 unstable metrics.

scenario:iast_aspects-aspect_iast_do_center

• 🟩 max_rss_usage [-2.715MB; -2.355MB] or [-9.129%; -7.918%]

scenario:iast_aspects-aspect_iast_do_index

• 🟩 max_rss_usage [-2.711MB; -2.353MB] or [-9.114%; -7.913%]

scenario:span-start-finish

• 🟩 execution_time [-7.324ms; -6.636ms] or [-12.927%; -11.712%]

scenario:span-start-finish-telemetry

• 🟩 execution_time [-6.481ms; -5.557ms] or [-11.094%; -9.513%]

scenario:span-start-finish-traceid128

• 🟩 execution_time [-6.803ms; -5.736ms] or [-11.275%; -9.506%]