(fix) internal/civisibility/utils: improve environment tags mutability (v2)

[tonyredondo]

What does this PR do?

This PR improves the mutability over the environment tags, avoiding to re-running the Cmds (git commands) after adding new tags and avoiding race conditions.

Same PR for main: #3076

Motivation

Currently if we add a new tag we end up by re running the git command to create a new map, this PR fixes this issue.

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: tony/civisibility-improve-environment-tags-mutability-v2
Commit report: 58680e8
Test service: dd-trace-go

✅ 0 Failed, 4079 Passed, 64 Skipped, 2m 48.21s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-10 16:52:34

Comparing candidate commit 78ac03f in PR branch tony/civisibility-improve-environment-tags-mutability-v2 with baseline commit 89bfc59 in branch v2-dev.

Found 2 performance improvements and 0 performance regressions! Performance is the same for 49 metrics, 2 unstable metrics.

scenario:BenchmarkInjectW3C-24

• 🟩 execution_time [-150.726ns; -115.874ns] or [-3.625%; -2.787%]

scenario:BenchmarkSetTagStringer-24

• 🟩 execution_time [-8.465ns; -3.275ns] or [-5.707%; -2.208%]