HTTP Request Instrumentation

### Description

First of, I'd like to say this is a great library and we're using it successfully in prod for a while now!

One thing I feel is missing is instructions on how to best instrument this. I see it uses [httpc](https://www.erlang.org/doc/apps/inets/httpc.html) to make the HTTP requests, but I can't find any docs online about how to get instrumentation data out of it (idk if it's even possible).

Maybe a simpler solution here would be a way to provide the HTTP client as a config option, so we can add instrumentation there?