Add native support for IPv6

[s01ipsist]

Is your feature request related to a problem? Please describe.
As of Feb 1, 2024 AWS are charging for IPv4 usage.
https://aws.amazon.com/blogs/aws/new-aws-public-ipv4-address-charge-public-ip-insights/
We run our build hosts in a public subnet to avoid usurious data charges of a NAT gateway.
As of Feb 1, we have seen a sizable uplift in costs due to IPv4 runtime hour usage which we'd rather avoid as we don't require IPv4 connectivity on these hosts.

Describe the solution you'd like
We'd like a single config option that allowed the entire stack to run on IPv6 only.

Describe alternatives you've considered
The existing stack already allows for VpcId and Subnets to be created independently and passed in as variables. It's unclear if this would be a viable option (and we haven't yet tested this path).

Additional context
Add any other context or screenshots about the feature request here.

[moskyb]

kia ora @s01ipsist! thanks for pointing out the impact of this. i see where you're coming from in adding an option for running the stack on IPv6. We'll take a look at this, but would encourage taking a look at the option of defining your own VPC/Subnet configuration in the meantime. if you come up with something that works well, feel free to make a PR.