fix(profiling): tag serialisation in HTTP exporter [backport 2.8]

[github-actions]

Backport 0bacde0 from #9032 to 2.8.

Ensure that the HTTP exporter does not fail to serialise the tags.

Addresses #8996.

Checklist

• Change(s) are motivated and described in the PR description
• Testing strategy is described if automated tests are not included in the PR
• Risks are described (performance impact, potential for breakage, maintainability)
• Change is maintainable (easy to change, telemetry, documentation)
• Library release note guidelines are followed or label changelog/no-changelog is set
• Documentation is included (in-code, generated user docs, public corp docs)
• Backport labels are set (if applicable)
• If this PR changes the public interface, I've notified @DataDog/apm-tees.

Reviewer Checklist

• Title is accurate
• All changes are related to the pull request's stated goal
• Description motivates each change
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Change is maintainable (easy to change, telemetry, documentation)
• Release note makes sense to a user of the library
• 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-9032-to-2.8
Commit report: c009fd6
Test service: dd-trace-py

✅ 0 Failed, 42 Passed, 1008 Skipped, 6m 58.36s Total duration (1h 15m 12s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-04-22 09:44:23

Comparing candidate commit c009fd6 in PR branch backport-9032-to-2.8 with baseline commit 274535c in branch 2.8.

Found 4 performance improvements and 7 performance regressions! Performance is the same for 190 metrics, 9 unstable metrics.

scenario:httppropagationextract-datadog_tracecontext_tracestate_not_propagated_on_trace_id_no_match

• 🟩 max_rss_usage [-742.473KB; -665.322KB] or [-3.392%; -3.040%]

scenario:httppropagationextract-full_t_id_datadog_headers

• 🟥 max_rss_usage [+480.849KB; +743.036KB] or [+2.262%; +3.496%]

scenario:httppropagationextract-invalid_priority_header

• 🟩 max_rss_usage [-767.586KB; -517.329KB] or [-3.507%; -2.363%]

scenario:httppropagationextract-wsgi_empty_headers

• 🟩 max_rss_usage [-971.101KB; -709.898KB] or [-4.472%; -3.269%]

scenario:httppropagationextract-wsgi_large_header_no_matches

• 🟥 max_rss_usage [+650.475KB; +743.394KB] or [+3.069%; +3.508%]

scenario:httppropagationextract-wsgi_large_valid_headers_all

• 🟥 max_rss_usage [+465.992KB; +732.498KB] or [+2.188%; +3.440%]

scenario:httppropagationextract-wsgi_medium_header_no_matches

• 🟥 max_rss_usage [+532.897KB; +677.471KB] or [+2.510%; +3.191%]

scenario:httppropagationextract-wsgi_medium_valid_headers_all

• 🟥 max_rss_usage [+559.406KB; +787.768KB] or [+2.638%; +3.715%]

scenario:httppropagationextract-wsgi_valid_headers_basic

• 🟩 max_rss_usage [-762.801KB; -685.954KB] or [-3.488%; -3.136%]

scenario:httppropagationinject-with_tags_invalid

• 🟥 max_rss_usage [+688.562KB; +740.942KB] or [+3.259%; +3.507%]

scenario:httppropagationinject-with_tags_max_size

• 🟥 max_rss_usage [+662.919KB; +721.939KB] or [+3.136%; +3.415%]