* caddyhttp: Make use of http.ResponseController
Also syncs the reverseproxy implementation with stdlib's which now uses ResponseController as well 2449bbb5e6
* Enable full-duplex for HTTP/1.1
* Appease linter
* Add warning for builds with Go 1.20, so it's less surprising to users
* Improved godoc for EnableFullDuplex, copied text from stdlib
* Only wrap in encode if not already wrapped
