Add S3 only entity and fix error to derive from Exception. (#127)

Author: Laren-AWS

aws_doc_sdk_examples_tools/config/entities.yaml

@@ -14,4 +14,5 @@ expanded_override:
   "&kms-keys;": "KMS keys"
   "&kms-keys-long;": "AWS KMS keys"
   "&S3long;": "Amazon Simple Storage Service"
+  "&S3only;": "S3"
   "&SLN;": "Amazon States Language"

aws_doc_sdk_examples_tools/entities.py

@@ -6,7 +6,7 @@
 
 
 @dataclass
-class EntityError:
+class EntityError(Exception):
     """
     Base error. Do not use directly.
     """