feat(ec2): support for client route enforcement for client VPN endpoint (#34405)

### Issue # (if applicable)

None

### Reason for this change

Cloudformation supports for configuring [client route enforcement](https://docs.aws.amazon.com/vpn/latest/clientvpn-admin/cvpn-working-cre.html) feature for client VPN endpoint.

### Description of changes

- Add `enableClientRouteEnforcement` prop to `ClientVpnEndpointProps`

### Describe any new or updated permissions being added

None

### Description of how you validated changes

Add both unit and integ tests.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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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: badmintoncryer