Fix updateAgentJobStatus so it returns something other than true if e.g. the row is not found in the dynamodb table

Author: kaleko

template.yaml

@@ -3905,7 +3905,16 @@ Resources:
           }
         }
       ResponseMappingTemplate: |-
-        true
+        #if($ctx.error)
+          $util.error($ctx.error.message, $ctx.error.type)
+        #end
+        
+        ## Return false if no item was updated (item not found)
+        #if(!$ctx.result)
+          false
+        #else
+          true
+        #end
 
   DeleteAgentJobResolver:
     Type: AWS::AppSync::Resolver