add rclone serve sftp

[asdffdsa6131]

hello and thanks,
please add rclone serve sftp.

thanks

[supervisitor]

@asdffdsa6131 : SFTP is implemented, I use this (App Version 1.7.4-ARM32, Rclone Version 1.44). When you configure a new remote it is the 3rd-last, labeled "SFTP/SSH". 😇😉