chore(docs): add request() example for conditionally reading the body

[styfle]

This relates to...

Documentation for dispatcher.request()

Rationale

It is very easy to cause a memory leak or even crash the process if you forget to handle the response body.

Changes

A new example showing how to conditionally reading the body

Features

N/A

Bug Fixes

N/A

Breaking Changes and Deprecations

N/A

Status

• [x] I have read and agreed to the Developer's Certificate of Origin
• [ ] Tested
• [ ] Benchmarked (optional)
• [x] Documented
• [ ] Review ready
• [ ] In review
• [ ] Merge ready

[mcollina]

@Ethan-Arrowood PTAL

[Ethan-Arrowood]

What about @styfle 's comment / question here: https://github.com/nodejs/undici/pull/3743#discussion_r1804918142

Is dump sufficient if the body is larger than its limit?