Feature request: Add `sftp open` command

[tangrufus]

• 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 sftp open <env> <site> which opens sftp gui clients.

Cyberduck example:

$ trellis sftp open production example.com --app=cyberduck
# Invoke `open sftp://web@111.222.333.444:22/srv/www/example.com/`

Additional context

Similar to:

• Add db open command with Playbook struct #100

• trellis-cli/cmd/alias.go

  Lines 48 to 49 in 5c59781

  	ssh: "{{ web_user }}@{{ ansible_host }}:{{ ansible_port | default('22') }}"
  	path: "{{ project_root | default(www_root + '/' + item.key) | regex_replace('^~\/','') }}/{{ item.current_path | default('current') }}/web/wp"

[swalkinshaw]

This seems like a pretty niche command to me. Would be a perfect fit for a plugin if we want to revisit that.

[tangrufus]

Done in https://github.com/ItinerisLtd/trellis-cyberduck