Add support for stage message types

docs/api.rst

@@ -1653,6 +1653,31 @@ of :class:`enum.Enum`.
         The system message sent when a user is given an advertisement to purchase a premium tier for
         an application during an interaction.
 
+        .. versionadded:: 2.2
+    .. attribute:: stage_start
+
+        The system message sent when the stage starts.
+
+        .. versionadded:: 2.2
+    .. attribute:: stage_end
+
+        The system message sent when the stage ends.
+
+        .. versionadded:: 2.2
+    .. attribute:: stage_speaker
+
+        The system message sent when the stage speaker changes.
+
+        .. versionadded:: 2.2
+    .. attribute:: stage_raise_hand
+
+        The system message sent when a user is requesting to speak by raising their hands.
+
+        .. versionadded:: 2.2
+    .. attribute:: stage_topic
+
+        The system message sent when the stage topic changes.
+
         .. versionadded:: 2.2
     .. attribute:: guild_application_premium_subscription