ec2: add ClientVpnEndpoint.ClientConnectOptions & SelfServicePortal (#1854)
ec2: add ClientVpnEndpoint.ClientConnectOptions & SelfServicePortal (#1854)

- Add EC2::ClientConnectOptions
- Add validation function for SelfServicePortal
- Support to specify a federated SelfServicePortal IdP
cloudtools/troposphere,cloudtools/troposphere