Support "Task timed out" warnings as HTTP 504-errors

Currently if Lambda functions have a timeout then you will not see any errors in Cloudwatch, while the user gets a 200 http response code with `{ errorMessage: 'Task timed out in 10.0 s'}`. 

This change will show 5XX errors in Cloudwatch.

To support this I need to copy all the default patterns in `serverless.yml` per function, so therefore I think this need to be a default setting, while this is not caused by the Serverless(/our) code but by AWS Lambda itself.

lib/plugins/aws/package/compile/events/apiGateway/lib/validate.js

@@ -29,7 +29,7 @@ const DEFAULT_STATUS_CODES = {
     pattern: '[\\s\\S]*\\[502\\][\\s\\S]*',
   },
   504: {
-    pattern: '[\\s\\S]*\\[504\\][\\s\\S]*',
+    pattern: '([\s\S]*\[504\][\s\S]*)|(^[Task timed out].*)',
   },
 };