feat: add an alarm with breaching data set for rds instance (#138)

Co-authored-by: Matt Dunster Jones <mattdunsterjones@Matts-MacBook-Air.local>

Author: mjonesbase2

lib/cfnguardian/resources/rds_instance.rb

@@ -11,6 +11,7 @@ def default_alarms
       alarm.evaluation_periods = 1
       alarm.comparison_operator = 'LessThanThreshold'
       @alarms.push(alarm)
+      alarm.treat_missing_data = 'breaching'
 
       alarm = CfnGuardian::Models::RDSInstanceAlarm.new(@resource)
       alarm.name = 'FreeStorageSpaceTask'