tracer: configure global tags via remote-config

[ahmed-mez]

What does this PR do?

AIT-8977

• Make global tags dynamic: support custom global tags via remote config
• Report RC capabilities for custom tags
• Report telemetry events on custom tag updates

Motivation

Better onboarding UX

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.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-11-23 13:52:54

Comparing candidate commit f1a81db in PR branch ahmed/dynamic-config-part7 with baseline commit 55aa930 in branch main.

Found 4 performance improvements and 0 performance regressions! Performance is the same for 35 metrics, 2 unstable metrics.

scenario:BenchmarkPartialFlushing/Enabled-24

• 🟩 execution_time [-12.137ms; -6.048ms] or [-4.179%; -2.082%]

scenario:BenchmarkSingleSpanRetention/no-rules-24

• 🟩 execution_time [-8.554µs; -5.661µs] or [-3.315%; -2.194%]

scenario:BenchmarkStartSpan-24

• 🟩 execution_time [-136.035ns; -88.965ns] or [-5.607%; -3.667%]

scenario:BenchmarkTracerAddSpans-24

• 🟩 execution_time [-138.269ns; -87.931ns] or [-3.333%; -2.120%]

[darccio]

@ahmed-mez Curiosity: any idea why the PR changes affect positively starting spans and flushing them? Also, how does the QA for this look like? Thanks!

[ahmed-mez]

@darccio I'm also curious about the perf improvements, I wasn't expecting them. As for the QA, this has been manually validated e2e + a good unit test coverage + the corresponding system-test is not ready yet but I tried it locally and it passes (the test itself requires some changes though).