Document stream request message activity type (#8512)

Author: advaith1

developers/resources/message.mdx

@@ -132,12 +132,13 @@ Type `19` and `20` are only available in API v8 and above. In v6, they are repre
 <ManualAnchor id="message-object-message-activity-types" />
 ###### Message Activity Types
 
-| Type         | Value |
-|--------------|-------|
-| JOIN         | 1     |
-| SPECTATE     | 2     |
-| LISTEN       | 3     |
-| JOIN_REQUEST | 5     |
+| Type           | Value |
+|----------------|-------|
+| JOIN           | 1     |
+| SPECTATE       | 2     |
+| LISTEN         | 3     |
+| JOIN_REQUEST   | 5     |
+| STREAM_REQUEST | 6     |
 
 <ManualAnchor id="message-object-message-flags" />
 ###### Message Flags