Feature request: Add `rsync` command

• I've read the guidelines for Contributing to Roots Projects
• This request isn't a duplicate of an existing request
• This is not a personal support request that should be posted on the Roots Discourse community

Summary

Add trellis rsync which transfers files between remote servers and local machines.

Example:

rsync -aP --numeric-ids -e "ssh -T -o Compression=no -x -p 22" 'web@111.222.333.444:/srv/www/example.com/shared/uploads/' /Users/me/Desktop/example.com/uploads/

Discussion

What subcommands / flags should we provide?

For reference: AWS CLI provides 3 different subcommands for moving files between s3 buckets and local machines:

aws s3 mv <source> <destation>
aws s3 sync <source> <destation>
aws s3 cp <source> <destation>

Possible solutions:

# rsync without --delete
trellis rsync cp <env> <site> <source> <destation>

trellis rsync cp production example.com shared/uploads/ /Users/me/Desktop/example.com/uploads/
==> rsync -aP --numeric-ids -e "ssh -T -o Compression=no -x -p 22" 'web@111.222.333.444:/srv/www/example.com/shared/uploads/' /Users/me/Desktop/example.com/uploads/

trellis rsync cp --user=admin production example.com /absolute/path/ /Users/me/Desktop/example.com/uploads/
==> rsync -aP --numeric-ids -e "ssh -T -o Compression=no -x -p 22" 'admin@111.222.333.444:/absolute/path/' /Users/me/Desktop/example.com/uploads/

# rsync with --delete
trellis rsync sync <env> <site> <source> <destation>

Start by comparing the proposed trellis rsync cp and trellis rsync sync entry points with the CLI's existing command conventions. Resolve the supported arguments, flags, local and remote path behavior, and whether deletion is allowed; done means the selected command produces the documented rsync transfer for the shown examples.