Following the approach described in ipfs#115, define a new method signature on `Command` that supports full processing of the `Response` object when text encoding is requested.

Add an encoding check and dispatch to DisplayCLI in local, http client, and http handler code paths.

Unblocks resolution of `encoding` option processing in multiple go-ipfs issues.

- ipfs/kubo#7050 json encoding for `ls`
- ipfs/kubo#1121 json encoding for `add`
- ipfs/kubo#5594 json encoding for `stats bw`

- When both PostRun (output transformer) and DisplayCLI (terminal output) are present, ensure that both are run.

`EmitResponse` helper in executor.go is invoked by both local and HTTP client executors: the client fibs the command.Run interface via anonymous function.

Close the channel immediately if it will never be used.