feat: add variable for private link integration when using with security groups

[dmitrijn]

Add support for API Gateway and NLB private integrations when using with security groups

https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-nlb-for-vpclink-using-console.html

https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lb#enforce_security_group_inbound_rules_on_private_link_traffic

[gberenice]

/terratest