Introduce a method to retrieve client IP address easily

Getting the client IP address is not trivial. It'd be great if you could expose functionality to retrieve IP address information easily. I frequently log this info for every API request. I'm not sure if reading `X-Forwarded-For` will always be supported.

https://stackoverflow.com/questions/37582553/how-to-get-client-ip-address-in-azure-functions-c

Looking at the answers, it's clear that IP address retrieval is pretty messy.