feature request: allow different type of subnets

[cao2504]

For the latestcdk v1 version, the default subnet type is set to Isolated instead of Private https://github.com/aws/aws-cdk/blob/master/packages/aws-cdk/lib/context-providers/vpcs.ts. When deploying the stack it will fail and complain about subnets are empty. Can we have a flexibility to choose which type of subnet to be passed in?

https://github.com/cloudcomponents/cdk-constructs/blob/28be2087009458aaa594aabe3d488dc3f4dd1815/packages/cdk-blue-green-container-deployment/src/ecs-service.ts#L138