fix(api): Web socket decode connection errors (#4606)

Author: Equartey

packages/api/amplify_api_dart/lib/src/graphql/web_socket/types/web_socket_types.dart

@@ -61,6 +61,7 @@ abstract class WebSocketMessagePayload {
     MessageType.connectionAck: ConnectionAckMessagePayload.fromJson,
     MessageType.data: SubscriptionDataPayload.fromJson,
     MessageType.error: WebSocketError.fromJson,
+    MessageType.connectionError: WebSocketError.fromJson,
   };
 
   static WebSocketMessagePayload? fromJson(

packages/api/amplify_api_dart/test/web_socket/web_socket_types_test.dart

@@ -65,6 +65,21 @@ void main() {
       },
       MessageType.error,
     ),
+    MessageTypeTestEntry(
+      {
+        'id': 'abc-456',
+        'type': 'connection_error',
+        'payload': {
+          'errors': [
+            {
+              'errorType': 'UnknownConnectionError',
+              'message': 'Unknown connection id abc-456',
+            }
+          ],
+        },
+      },
+      MessageType.connectionError,
+    ),
   ];
 
   group('WebSocketMessage should create expected messages from JSON', () {