contrib/net/http: Adding an example for wrap client

[ajgajg1134]

What does this PR do?

Adds an example for connecting a net/http handler to an outgoing call using net/http Client

Motivation

Recently had a colleague reach out trying to do this. In the process of helping them I realized our documentation for how to do this is lacking. I'm hoping adding this example and a link to it from the ddtrace docs will make this easier / less error-prone for customers.

Describe how to test/QA your changes

No QA needed

Reviewer's Checklist

• If known, an appropriate milestone has been selected; otherwise the Triage milestone is set.
• Changed code has unit tests for its functionality.
• If this interacts with the agent in a new way, a system test has been added.

[pr-commenter]

Benchmarks

Comparing candidate commit 7d6b835 in PR branch andrew.glaude/netHttpDocs with baseline commit 1878514 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 6 cases.