Support https_only Requests

[elichai]

Right now https_only is something set in the Client when building it, this means that if you have a dynamic runtime configuration you need to either re-build the Client each time, or hold 2 clients and choose between them.
It would be nicer if RequestBuilder had that configuration so it could be chosen per request, and not just per Client.

(Specifically, we want to force that if a user used a https scheme, we force the connection to be https, disallowing e.g. A redirection to http.

[seanmonstar]

That sounds like it could also be controlled with a custom redirect policy, perhaps?

[RowanCole]

A custom redirect policy only handles HTTP interception for redirect targets and cannot fully emulate https_only. Using it as a makeshift security control creates residual security vulnerabilities, and it cannot address the core requirement of selecting policies per request rather than per client.