fix(cloudwatch): return empty CompositeAlarms and LogAlarms from DescribeAlarms (#6363)

* fix(cloudwatch): return empty CompositeAlarms and LogAlarms from DescribeAlarms

AWS sends every alarm collection even when it is empty. Floci only sent
MetricAlarms, so the AWS CLI's text output printed a leading None line
for each missing paginator result key.

Closes #6362

* test(cloudwatch): check empty alarm collections in sdk-test-python instead of bats

Drop the new AWS CLI bats file and assert the empty CompositeAlarms and
LogAlarms lists in the existing describe_alarms test, as boto3 leaves an
absent list out of the response.

(cherry picked from commit 42f5019231b446c727d6c94def9d1445263de2d7)

compatibility-tests/sdk-test-python/tests/test_cloudwatch.py

@@ -203,6 +203,8 @@ class TestCloudWatchAlarms:
 
             alarm = next(a for a in alarms if a["AlarmName"] == alarm_name)
             assert alarm["StateValue"] == "INSUFFICIENT_DATA"
+            assert response["CompositeAlarms"] == []
+            assert response["LogAlarms"] == []
         finally:
             cloudwatch_client.delete_alarms(AlarmNames=[alarm_name])