envoyproxy: body parsing support

[e-n-0]

What does this PR do?

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 golangci-lint run 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.

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[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2025-06-26 21:38:36

Comparing candidate commit 399ea9ea27fc6798205739d1deca1f0f4b69e419 in PR branch flavien/envoy/body-parsing with baseline commit cb65a924f4f021342fdab20bd483af5f7a7921fc in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.

[datadog-datadog-prod-us1[bot]]

Datadog Report

Branch report: flavien/envoy/body-parsing Commit report: e922080 Test service: dd-trace-go

:white_check_mark: 0 Failed, 5420 Passed, 66 Skipped, 4m 25.85s Total Time