Wrap up work from #3895

Basically this PR was required for Cillium on EKS - we got the functionality merged but no docs.

We should have documentation for the new helm fields here:
https://agones.dev/site/docs/installation/install-agones/helm/

And also an update to our EKS guide:
https://agones.dev/site/docs/installation/creating-cluster/eks/