rpcclient: custom http client for http post mode

[therealssj]

Problem

The rpcclient only allows you configure the http client but there is no way to set my own http client so if I want to define my own custom transport its not possible.

Solution
simple function to set the httpClient directly

btcd/rpcclient/infrastructure.go

Line 152 in c4f3999

httpClient *http.Client

I would be happy to do a PR if this suggestion is approved

[jakesylvestre]

@therealssj please take a stab at the PR. Can't wait to see what you come up with!

[jcvernaleo]

As a general rule, we don't 'approve' suggestions. We can certainly discuss suggestions, but ultimately, we either approve or deny PRs. Obviously there are some suggestions that are far enough off from what we want that we can say we are very unlikely to accept a PR for it, but generally, it is code we evaluate.