fix(core): add RetainExceptOnCreate to ParseDeletionPolicy method (#26880)

> Describe the reason for this change, what the solution is, and any

CFN recently added support for a new [deletion policy called RetainExceptOnCreate](https://aws.amazon.com/about-aws/whats-new/2023/07/aws-cloudformation-deletion-policies-dev-test-cycle/). This policy was added to the removal-policy enum in [e0d5ca](e0d5cad), however it is missing from the [switch/case block in parseDeletionPolicy](https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/core/lib/helpers-internal/cfn-parse.ts#L468), which causes errors when this removal policy is used.


Closes #26863.

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: dineshkatamneni

packages/aws-cdk-lib/core/lib/helpers-internal/cfn-parse.ts

@@ -472,6 +472,7 @@ export class CfnParser {
       case 'Delete': return CfnDeletionPolicy.DELETE;
       case 'Retain': return CfnDeletionPolicy.RETAIN;
       case 'Snapshot': return CfnDeletionPolicy.SNAPSHOT;
+      case 'RetainExceptOnCreate': return CfnDeletionPolicy.RETAIN_EXCEPT_ON_CREATE;
       default: throw new Error(`Unrecognized DeletionPolicy '${policy}'`);
     }
   }