fix(ddtrace/tracer): refactor DogStatsD URL resolution using agent-reported StatsD port

[darccio]

What does this PR do?

It's a follow-up from #2931, that introduced a new behaviour to make sure metrics are reported properly by overriding any user-provided host:port address using the agent-reported StatsD port from the agent /info endpoint.

Motivation

Fixing a bug causing runtime metrics to not be reported when using WithDogstatsdAddr with UDS paths.

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.
• 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!

[darccio]

Just some housekeeping. Linting reported this type as unused.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-11-27 14:35:55

Comparing candidate commit 9a69867 in PR branch dario.castane/incident-32698-followup with baseline commit e9a64d3 in branch main.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 57 metrics, 1 unstable metrics.

scenario:BenchmarkHttpServeTrace-24

• 🟩 execution_time [-459.831ns; -400.169ns] or [-2.829%; -2.462%]