feat: enable process tags by default

[raphaelgavache]

What does this PR do?

Setting process tags collection on by default

The process tag collection is already enabled on couple go applications, and is on by default for the java tracer on many many applications. (on my default on jvm 21 for 1.53.0, always on by default for 1.54+)

matching system tests: DataDog/system-tests#5382

next follow-ups

• add tags in runtime metrics
• support container back propagation for DSM/DBM

NB - The following performance check fail with a 25% addition in alloc . This can be fixed as they are tracer level tags that can be injected only once on first span of the first chunk in an encoded message.
Attempt to perf fix the issue: #4010

Motivation

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.
• New code is free of linting errors. You can check this by running ./scripts/lint.sh locally.
• 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!

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-01 00:22:10

Comparing candidate commit a22f108 in PR branch raphael/process_tags_default with baseline commit 2997dc9 in branch main.

Found 0 performance improvements and 3 performance regressions! Performance is the same for 3 metrics, 0 unstable metrics.

scenario:BenchmarkOTelApiWithCustomTags/datadog_otel_api-24

• 🟥 allocated_mem [+849 bytes; +858 bytes] or [+25.038%; +25.283%]

scenario:BenchmarkOTelApiWithCustomTags/otel_api-24

• 🟥 allocated_mem [+836 bytes; +852 bytes] or [+17.717%; +18.062%]
• 🟥 execution_time [+332.065ns; +397.735ns] or [+4.408%; +5.279%]

[kakkoyun]

LGTM