Feature: Add support for SFTP

[Tombstone2K]

Requirements

• Enabled add new SFTP connections (should follow the same UX as FTP)

[benjione]

I think this is a duplicate of #1629 and was merged with #1342 . However, FTP is not the same as SFTP. I suggest merging this with #1342 .

[ttmx]

This would be extremely nice and would remove the need for Filezilla and the likes, making it a much more uniform and convenient experience.