AWS::EC2::VPNConnection - [Feature Request] - Missing support for PreSharedKeyStorage

### Name of the resource

AWS::EC2::VPNConnection

### Resource name

_No response_

### Description

Scope: New attribute (PreSharedKeyStorage) is required for existing resource AWS::EC2::VPNConnection.

This attribute is currently available in CLI (create-vpn-connection) and API (API_CreateVpnConnection) but missing in Cloudformation. The requirement is to provide [enhanced security features ](https://docs.aws.amazon.com/vpn/latest/s2svpn/enhanced-security.html)for site to site VPN resources provisioned via cloudformation. We would want to store the pre-shared key in a secretsmanager secret.

### Other Details

Cloudformation reference - https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-resource-ec2-vpnconnection.html

API doc - https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_CreateVpnConnection.html

CLI doc - https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/create-vpn-connection.html

Start with the AWS::EC2::VPNConnection CloudFormation reference, then compare the CreateVpnConnection API and create-vpn-connection CLI documentation linked in the issue. Done means the resource supports the PreSharedKeyStorage attribute and allows the pre-shared key to be stored in a Secrets Manager secret.

Written by the indexing model from the issue text.