new NewPooledClient for people who need keepalive

[painhardcore]

A new client for retrier fo the same host with keepalive

[ryanuber]

Hey @painhardcore, thanks for the PR!

Cases like this are exactly why we have made the HTTPClient field public - so that any client configuration under the sun can be applied to the retrying HTTP client! For these kinds of use cases I think it's best if you create a new client and apply your specific configuration to it prior to making the first request. This keeps the API surface area of retryablehttp minimal while still allowing the flexibility you are after.

I'm going to close this for that reason, thanks again for contributing!