internal/remoteconfig: support for DD_REMOTE_CONFIGURATION_ENABLED

[eliottness]

What does this PR do?

Introduces a new env var called DD_REMOTE_CONFIGURATION_ENABLED to disable remote config client side.

Motivation

Closes #3060

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: eliottness/DD_REMOTE_CONFIGURATION_ENABLED
Commit report: 6cde583
Test service: dd-trace-go

✅ 0 Failed, 5121 Passed, 70 Skipped, 2m 54.57s Total Time
❄️ 1 New Flaky

New Flaky Tests (1)

• TestExchangeContext - gopkg.in/DataDog/dd-trace-go.v1/contrib/miekg/dns

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-02 11:08:22

Comparing candidate commit d9ea482 in PR branch eliottness/DD_REMOTE_CONFIGURATION_ENABLED with baseline commit 4f57a47 in branch main.

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