Enable S3 event fanout using SNS

[jpaolin]

A legitimate case could be made around fanning out S3 events using SNS, with the Lambda function as one of the subscribers. We would have to handle both S3 and SNS events as potential triggers.

Example S3 event

{  
   "Records":[  
      {  
         "eventVersion":"2.0",
         "eventSource":"aws:s3",
         "awsRegion":"us-east-1",
         "eventTime":"1970-01-01T00:00:00.000Z",
         "eventName":"ObjectCreated:Put",
         "userIdentity":{  
            "principalId":"AIDAJDPLRKLG7UEXAMPLE"
         },
         "requestParameters":{  
            "sourceIPAddress":"127.0.0.1"
         },
         "responseElements":{  
            "x-amz-request-id":"C3D13FE58DE4C810",
            "x-amz-id-2":"FMyUVURIY8/IgAtTv8xRjskZQpcIZ9KG4V5Wp6S7S/JRWeUWerMUE5JgHvANOjpD"
         },
         "s3":{  
            "s3SchemaVersion":"1.0",
            "configurationId":"testConfigRule",
            "bucket":{  
               "name":"mybucket",
               "ownerIdentity":{  
                  "principalId":"A3NL1KOZZKExample"
               },
               "arn":"arn:aws:s3:::mybucket"
            },
            "object":{  
               "key":"HappyFace.jpg",
               "size":1024,
               "eTag":"d41d8cd98f00b204e9800998ecf8427e",
               "versionId":"096fKKXTRTtl3on89fVO.nfljtsv6qko",
               "sequencer":"0055AED6DCD90281E5"
            }
         }
      }
   ]
}

Example SNS event

{
  "Records": [
    {
      "EventVersion": "1.0",
      "EventSubscriptionArn": "arn:aws:sns:EXAMPLE",
      "EventSource": "aws:sns",
      "Sns": {
        "SignatureVersion": "1",
        "Timestamp": "1970-01-01T00:00:00.000Z",
        "Signature": "EXAMPLE",
        "SigningCertUrl": "EXAMPLE",
        "MessageId": "95df01b4-ee98-5cb9-9903-4c221d41eb5e",
        "Message": "Hello from SNS!",
        "MessageAttributes": {
          "Test": {
            "Type": "String",
            "Value": "TestString"
          },
          "TestBinary": {
            "Type": "Binary",
            "Value": "TestBinary"
          }
        },
        "Type": "Notification",
        "UnsubscribeUrl": "EXAMPLE",
        "TopicArn": "arn:aws:sns:EXAMPLE",
        "Subject": "TestInvoke"
      }
    }
  ]
}