s3 datasource: add sns format (#820)

Author: blotus

crowdsec-docs/docs/log_processor/data_sources/s3.md

@@ -67,7 +67,7 @@ Required when `polling_method` is `sqs`.
 ### `sqs_format`
 
 Format of the body inside the SQS messages.
-Can be `eventbridge` or `s3notification`.
+Can be `eventbridge`, `s3notification` or `sns`.
 
 If not set, the Security Engine will automatically select the format based on the first valid event received from the queue.