contrib/net/http: implement rwUnwrapper

[rarguelloF]

What does this PR do?

Fixes #2674

Implement the rwUnwrapper interface for the wrapped http.ResponseWriter we return in this package.

Motivation

The rwUnwrapper interface is checked and used internally in the standard library: https://github.com/golang/go/blob/6d89b38ed86e0bfa0ddaba08dc4071e6bb300eea/src/net/http/responsecontroller.go#L42-L44

This approach makes unnecessary to implement all the possible http.ResponseWriter optional methods in the wrapped type.

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: 2024-07-08 16:06:22

Comparing candidate commit f751181 in PR branch rarguelloF/AIDM-199/fix-net-http-rw-timeouts with baseline commit dc5c6a9 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 47 metrics, 0 unstable metrics.