ddtrace/tracer: Support DD_DOGSTATSD_HOST env var

[mtoffl01]

What does this PR do?

Allows use of DD_DOGSTATSD_HOST env var to specify destination of the statsd client. Takes precedence over DD_AGENT_HOST for the statsd client.

Motivation

Config Consistency: Ref.

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.
• For internal contributors, a matching PR should be created to the v2-dev branch and reviewed by @DataDog/apm-go.

Unsure? Have a question? Request a review!

[datadog-datadog-prod-us1]

Datadog Report

Branch report: mtoff/dogstatsd-host
Commit report: 8f1b4b1
Test service: dd-trace-go

✅ 0 Failed, 5135 Passed, 70 Skipped, 2m 30.18s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-14 20:57:02

Comparing candidate commit 48adfed in PR branch mtoff/dogstatsd-host with baseline commit 471d723 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 59 metrics, 0 unstable metrics.