Closes#478 The mode option of fs.writeFile does not reliably apply
permissions on all filesystems. On Synology NAS Docker volumes (btrfs),
the file ends up with 0755 permissions instead of 0600, causing SSH to
refuse the key.
* feat: add support for SFTP volume backend
* feat: allow more secure SFTP connection with known hosts
* refactor: make default value for skip host key check to false
* refactor: use os.userInfo when setting uid/gid in mount commands