client-api: Update leave_room to new API conventions

ruma-client-api/src/r0/membership/leave_room.rs

@@ -16,10 +16,24 @@ ruma_api! {
     request: {
         /// The room to leave.
         #[ruma_api(path)]
-        pub room_id: RoomId,
+        pub room_id: &'a RoomId,
     }
 
     response: {}
 
     error: crate::Error
 }
+
+impl<'a> Request<'a> {
+    /// Creates a new `Request` with the given room id.
+    pub fn new(room_id: &'a RoomId) -> Self {
+        Self { room_id }
+    }
+}
+
+impl Response {
+    /// Creates an empty `Response`.
+    pub fn new() -> Self {
+        Self
+    }
+}