Implement DD_TRACE_LOG_DIRECTORY

[mtoffl01]

What does this PR do?

Supports specifying a log directory for tracer logs via DD_TRACE_LOG_DIRECTORY env var. If directory exists on the underlying os, tracer creates log file ddtrace.log at specified path and all tracer logs are routed to said file. Tracer maintains default behavior (log to stdout) if directory is invalid or does not exist.

Motivation

Bring dd-trace-go up to speed on feature parity (other tracing libs support this). RFC

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.

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[pr-commenter]

Benchmarks

Benchmark execution time: 2024-10-07 21:21:53

Comparing candidate commit a9d646d in PR branch mtoff/trace-log-directory with baseline commit 2a34b15 in branch main.

Found 0 performance improvements and 1 performance regressions! Performance is the same for 58 metrics, 0 unstable metrics.

scenario:BenchmarkInjectW3C-24

• 🟥 execution_time [+91.751ns; +136.649ns] or [+2.249%; +3.350%]