Now, the command for `jj git remote add` is `cmd_git_remote_add` and its
argument type is `GitRemoteAddArgs`. This should make it easier to find
the CLI docs and the implementation for commands.
This is how `jj branch` commands were already set up in this way. The
`jj op` commands were also already set up in this way, except the
functions are called e.g. `cmd_op_undo`, I kept this for simplicity.
I was mainly motivated by the `jj file` commands. Most other commands
had functions already named in the above pattern, but used to have
shorter argument type names.
