Fix for regions where resource policy not supported to not throw error during create

[vramanet]

Currently we are seeing error during create namespace in regions where resource policy is not enabled. If a customer provides a resource policy during create and that region doesnt support resource policy we should not throw any error.

Testing:

1. Tested in region us-west-1 where resource policy API is not supported yet.
2. enable virtualenv
3. cd aws-redshiftserverless-namespace && sam local start-lambda
4. In anothet terminal enable virtualenev
5. cfn invoke resource CREATE local-tests-artifacts/create-aws-redshiftserverless-namespace.json

Results:
cfn=== Handler response ===
{
"status": "SUCCESS",
"callbackDelaySeconds": 0,
"resourceModel": {
"AdminUsername": "admin",
"DbName": "dev",
"IamRoles": [],
"KmsKeyId": "AWS_OWNED_KMS_KEY",
"LogExports": [
"userlog"
],
"Namespace": {
"NamespaceArn": "arn:aws:redshift-serverless:us-west-1:254260483320:namespace/491ac828-97a8-4ed2-b7b1-f5f242a694a3",
"NamespaceId": "491ac828-97a8-4ed2-b7b1-f5f242a694a3",
"NamespaceName": "ns-cfn-vramanet-test-xs7mtkvog2zfey",
"AdminUsername": "admin",
"DbName": "dev",
"KmsKeyId": "AWS_OWNED_KMS_KEY",
"IamRoles": [],
"LogExports": [
"userlog"
],
"Status": "AVAILABLE",
"CreationDate": "2024-02-08T11:55:45.950Z"
},
"NamespaceName": "ns-cfn-vramanet-test-xs7mtkvog2zfey"
}
}

Issue #, if available:

Description of changes:

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