Enable private DNS resolution on peered VPCs using CloudFormation

Hi, I see in the CloudFormation Public Roadmap, this issue https://github.com/aws-cloudformation/cloudformation-coverage-roadmap/issues/169 is still outstanding. A CDK custom workaround is mentioned there, but it would be possible in CloudFormation using a Resource Type or Custom Resource, calling this API - https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_ModifyVpcPeeringConnectionOptions.html.

I find that for situations where a Custom Resource is well-suited it's really quick to implement via a Python lambda using crhelper (https://github.com/aws-cloudformation/custom-resource-helper) described at https://aws.amazon.com/blogs/infrastructure-and-automation/aws-cloudformation-custom-resource-creation-with-python-aws-lambda-and-crhelper/).