Update ai validator ecs configuration (#151)

*Issue #, if available:*
The ECS tasks are failing due to not enough disk space. Also the alarms
are showing as success despite no metrics being available due to the ECS
task failures

*Description of changes:*
- Increased ECS disk space from 20gib to 40 gib
- Changing alarm to consider missing data point as breaching

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Author: harrryr

ai-validator/cdk/ecs.ts

@@ -102,6 +102,7 @@ export class AIValidatorStack extends cdk.Stack {
         cpu: 4096,
         memoryLimitMiB: 8192,
         taskRole,
+        ephemeralStorageGiB: 40,
       });
 
       taskDef.addContainer(`AITestContainer-${testId}`, {
@@ -162,7 +163,7 @@ export class AIValidatorStack extends cdk.Stack {
         evaluationPeriods: 1,
         comparisonOperator:
           cloudwatch.ComparisonOperator.GREATER_THAN_OR_EQUAL_TO_THRESHOLD,
-        treatMissingData: cloudwatch.TreatMissingData.NOT_BREACHING,
+        treatMissingData: cloudwatch.TreatMissingData.BREACHING,
       });
 
       failureAlarms.push(alarm);