Add support for network address usage metrics

[lanzrein]

what

This PR adds support for Network Address Usage Metrics on the VPC. AWS documentation : https://docs.aws.amazon.com/vpc/latest/userguide/network-address-usage.html Terraform documentation : https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/vpc#enable_network_address_usage_metrics

why

Network Address Usage metrics can help monitor the growth of a VPC and would be useful for any user. Enable this after creating a VPC does not trigger recreation of the VPC.

references

closes #115

[lanzrein]

Hello, This is my first PR on this repository. Please let me know if I need to do any other things to make the process smoother on your side.

[joe-niland]

/terratest