[fud2] Add subcommand to edit configuration

[rachitnigam]

Similar to fud c --edit but does not support querying keys yet. Tagging @sampsyo for visibility.

[sampsyo]

Seems useful! One thing UI to chat about here: so far, I hadn't added subcommands to the CLI. The main goal was to avoid the need for the e we in practice need to use for every OG fud invocation. I hadn't really thought of optional subcommands, but it makes sense. I guess I would have done something like fud2 --edit-config or something if I had done it, but I don't object to fud2 edit-config either. (It doesn't seem to add any ambiguity, because fud2 edit-config isn't a reasonable build command even if you have a file called edit-config for whatever reason, because we don't know the output state.)

[rachitnigam]

Yeah, I think getting rid of e is a good idea. I was implicitly going with the philosophy that "management options" like editing the config or something like fud check can be commands while other things are not.

[sampsyo]

Sounds legit. After all, for stuff like that, all the other CLI options (e.g., --from, -o) are irrelevant, so it would be a weird lie to make them "siblings" to those.