This command is confusing in name and function. Rather than creating
a hard fork of a repository, with a new identity, it pushes the
default branch to the local user's namespace.
Deprecate it and add some help text.
Now that all commands can be parsed by clap, remove any custom parsing and
directly use `CliArgs::parse`.
The `Diff` command was removed, since only one `external_command` can be
declared for a subcommand. The handling of `rad diff` is now done via the
`External` variant. If the subcommand name is `diff` then this is executed,
otherwise delegate to the possible `rad-{exe}` command.
Also of note, the `rad inspect` command has an alias `rad .`. This changes the
behaviour of `rad . --help`. Before, it would print the help of the `rad`
command. Now, it prints the help of `rad inspect`.
Co-authored-by: Lorenz Leutgeb <lorenz.leutgeb@radicle.xyz>