[AWS::SecretsManager::Secret] - [Enhancement] - Support --import-existing-resources

### Name of the resource

AWS::SecretsManager::Secret

### Resource name

_No response_

### Description

An SecretsManager::Secret is an obvious resource to set as:
```json
"UpdateReplacePolicy" : "Retain",
"DeletionPolicy" : "RetainExceptOnCreate"
```

e.g. if it's a pepper used to hash values stored persistently - that secret cannot change.

However, because its `primariyIdentifier` is `Id` and `Id` is a read only property it cannot be imported using `--import-existing-resources`. So if you created the secret via CloudFormation (or the CDK) and want to recreate the stack using the same secret it does not work trivially.

### Other Details

_No response_

Start with the AWS::SecretsManager::Secret entry and the --import-existing-resources behavior described here, paying attention to its read-only primaryIdentifier Id and the stated UpdateReplacePolicy and DeletionPolicy use. Done means a retained secret created by CloudFormation or CDK can be reused when recreating the stack through --import-existing-resources.

Written by the indexing model from the issue text.