feat(cloudwatch): support composite alarm lifecycle (#6408)

(cherry picked from commit 922e36a472341861e97d1b5639656f3c4a3978d8)

tools/docs/cfn_resource_types.yaml

@@ -169,6 +169,9 @@ notes:
 # Trailing prose appended to a row after its type list, for behaviour that belongs to the service
 # rather than to one type.
 row_notes:
+  AWS::CloudWatch: >-
+    Composite alarms have backing definitions with name Ref and Arn GetAtt, rollback, and
+    replacement cleanup. Composite actions are stored only; suppression properties are rejected.
   AWS::Lambda: >-
     Inline `ZipFile` packages include the `cfn-response` (Node.js) / `cfnresponse` (Python) module
     AWS injects for that code path, so Solutions-style custom-resource handlers work.