AWS GWLB Support

[ozcrn]

Adds initial support for AWS Gateway Load Balancer integration utilising aws-gateway-load-balancer-tunnel-handler

Implements feature request #92

[ddouglas]

I get the idea behind this, but building this software in the same ami that is running in production feels wrong. This software should be compiled for this os and arch, hosted in Github Packages or S3, and then downloaded onto the box during fcknats ami build.

With the current way this is setup, all the build requirements are persisted to the final image. Additionally, there is no way to disable this functionality. If i as a consumer of fcknat don't want or need this feature, I still have to deal with it existing on the ec2 instance I deploy

[AndrewGuenther]

I agree with @ddouglas about the build deps, but we also don't have good support (yet) in our build process for building these dependencies elsewhere. We've got the same problem with NAT64 support. Given that we've got two use cases now, I'll work on cooking something up.

Overall, this is great and I'm excited to start testing it out!