feat: add command output/error option

[schomatis]

Add an option to save command output to a file instead of the stdout argument (which was always set to stdout by go-ipfs consumer). We have removed the option and assumed stdout except the option is set (this was intended to loudly flag the output is being set by an option since the argument could be misleadingly overridden, but we can restore the argument and have the two coexist).

Used in https://github.com/ipfs/go-ipfs/pull/8683.

Related to https://github.com/ipfs/go-ipfs/issues/8335.

[schomatis]

@lidel Added error output option (we can review the option names at the end; I'm leaving for now the conspicuous --command-output/error for visibility).