update Subnets

[vincentsarago]

This PR does:

• adds specific subnets configuration to the vpc
• assign each resource to a specific subnets
• add nat_gateways to enable the lambda to connect to the outside world ($$$$)

[vincentsarago]

ping @edkeeble @sharkinsspatial 👋

I've been reading a bit more on nat_gateways. It seems the best/easy solution, but it seems we could also do:

• create a small ec2 instance to serve a bastion/nat-gateway (price should be ~15$/month, instead of 35$/month)
• still use ec2 but with something like https://registry.terraform.io/modules/int128/nat-instance/aws/latest (the cdk equivalent seems to be https://github.com/fonzcastellanos/cdk-nat-asg-provider)

ref:

• https://www.cloudforecast.io/blog/aws-nat-gateway-pricing-and-cost/
• https://www.reddit.com/r/aws/comments/lfsfze/nat_gateway_in_vpc_with_lambda_costly/