Add a Gateway VPC endpoint for S3

NatGateway has a pretty hefty fee for data transfer. To avoid those costs, S3 can use a custom route through a Gateway VPC Endpoint.
>Best practice when sending traffic to Amazon S3 or DynamoDB in the same Region
>To avoid data processing charges for NAT gateways when accessing Amazon S3 and DynamoDB that are in the same Region, set up a gateway endpoint and route the traffic through the gateway endpoint instead of the NAT gateway. There are no charges for using a gateway endpoint. For more information, see Gateway VPC endpoints.
[1](https://docs.aws.amazon.com/vpc/latest/userguide/vpc-nat-gateway.html)

Main docs for [gateway endpoints](https://docs.aws.amazon.com/vpc/latest/userguide/vpce-gateway.html#vpc-endpoints-limitations) *Note* in this case S3 does need to be same region as the ECS/Fargate instance to use. Otherwise we still have the NatGateway costs and the Cross Region costs.

CDK has a construct [GatewayVPCEndpoint](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-ec2.GatewayVpcEndpoint.html)