aws-fms:CfnPolicy: Missing example for AntiDDos rule

### Describe the issue

Hi.

I am trying to create a Policy with the AWSManagedRulesAntiDDoSRuleSet.

The documentation does not contain an example and I keep getting the following error when I deploy the stack.

`Resource handler returned message: "AWSManagedRulesAntiDDoSRuleSet can't have null or empty ManagedRuleGroupConfigs.`

even through the the ManagedRuleGroupConfigs is containing an array with a AWSManagedRulesAntiDDoSRuleSet.

I am adding the following json to the managedServiceData property as a string.

```json
{
"type": "WAFV2",
"preProcessRuleGroups": [
{
"overrideAction": { "type": "NONE" },
"ruleGroupType": "ManagedRuleGroup",
"ruleGroupArn": null,
"excludeRules": [],
"ruleActionOverrides": [
{ "name": "ChallengeAllDuringEvent", "actionToUse": { "count": {} } },
{ "name": "ChallengeDDoSRequests", "actionToUse": { "count": {} } },
{ "name": "DDoSRequests", "actionToUse": { "count": {} } }
],
"ManagedRuleGroupConfigs": [
{
"AWSManagedRulesAntiDDoSRuleSet": {
"ClientSideActionConfig": {
"Challenge": {
"UsageOfAction": "ENABLED",
"Sensitivity": "HIGH",
"ExemptUriRegularExpressions": [
{
"RegexString": [\\/api\\/|\\.(acc|avi|css|gif|ico|jpe?g|js|json|mp[34]|ogg|otf|pdf|png|tiff?|ttf|webm|webp|woff2?|xml)$](x-webdoc://6CAED313-A56A-4DDF-8258-EB531335EA4D/api/|/.(acc|avi|css|gif|ico|jpe?g|js|json|mp%5b34%5d|ogg|otf|pdf|png|tiff?|ttf|webm|webp|woff2?|xml)$)
}
]
}
},
"SensitivityToBlock": "LOW"
}
}
],
"managedRuleGroupIdentifier": {
"vendorName": "AWS",
"managedRuleGroupName": "AWSManagedRulesAntiDDoSRuleSet",
"version": null
}
}
],
"postProcessRuleGroups": [],
"defaultAction": { "type": "ALLOW" },
"overrideCustomerWebACLAssociation": false,
"VisibilityConfig": {
"SampledRequestsEnabled": true,
"CloudWatchMetricsEnabled": true,
"MetricName": "FmsPublicMetricGlobalNonProd"
}
}

```

Can anyone provide me with a working example or explain to me what is wrong.

### Links

https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_fms.CfnPolicy.SecurityServicePolicyDataProperty.html#managedservicedata

Start with the linked CfnPolicy.SecurityServicePolicyDataProperty API documentation and the managedServiceData section, then compare its documented structure with the AWSManagedRulesAntiDDoSRuleSet payload in the issue. Done means the documentation includes a valid working example or clearly explains the required ManagedRuleGroupConfigs structure and resolves the reported deployment error.

Written by the indexing model from the issue text.