limactl copy should use rsync instead of scp for copying a directory

[AkihiroSuda]

Description

limactl copy should use rsync (present on macOS by default) instead of scp for copying a directory.
scp might be still faster for small directories, but probably the overhead is subtle.

lima/cmd/limactl/copy.go

Line 47 in eebc684

arg0, err := exec.LookPath("scp")

[afbjorklund]

You could make it optional, like we ended up doing for docker-machine scp?

Usage: docker-machine scp [OPTIONS] [arg...]

Copy files between machines

Description:
   Arguments are [[user@]machine:][path] [[user@]machine:][path].

Options:
   
   --recursive, -r	Copy files recursively (required to copy directories)
   --delta, -d		Reduce amount of data sent over network by sending only the differences (uses rsync)
   --quiet, -q		Disables the progress meter as well as warning and diagnostic messages from ssh

(my suggestion was --rsync, since it does has some rather tricky semantics)

Main reason is that it would require to install rsync on the guest as well...

[ayushgml]

@AkihiroSuda Can I work on this?

[afbjorklund]

I found that I had to add --progress, to make the rsync output more similar to scp default output:

a63be72