fs: add --all to rclone config create/update to ask all the config questions #3455

This also factors the config questions into a state based mechanism so
a backend can be configured using the same dialog as rclone config but
remotely.

fs/config/rc.go

@@ -118,6 +118,7 @@ func init() {
     - noObscure - declare passwords are already obscured and don't need obscuring
     - nonInteractive - don't interact with a user, return questions
     - continue - continue the config process with an answer
+    - all - ask all the config questions not just the post config ones
 `
 		}
 		rc.Add(rc.Call{