Add alert for failed events after retry and fix broken cloud event exception handling

Relates #3 (closed)

example/main.py

@@ -25,7 +25,7 @@ def example_raw_event_fail(raw_event):
 
     patch_me(raw_event)
 
-    return "", 501
+    raise ucam_faas.exceptions.UCAMFAASCouldNotProcess
 
 
 @ucam_faas.cloud_event
@@ -44,15 +44,6 @@ def example_cloud_event_fail(cloud_event):
     raise ucam_faas.exceptions.UCAMFAASCouldNotProcess
 
 
-@ucam_faas.cloud_event
-def example_cloud_event_fail_direct(cloud_event):
-    logger.info("got_cloud_event_fail", cloud_event=cloud_event)
-
-    patch_me(cloud_event)
-
-    return "", 501
-
-
 @ucam_faas.cloud_event
 def example_cloud_event_sometimes_fail(cloud_event):
     logger.info("got_cloud_event_fail", cloud_event=cloud_event)