Upgrade EKS Terraform configuration

[Grigory]

EKS module (starting v0.18) has a significant configuration change. This PR is to track down the progress of upgrading EKS Terraform module up to the most recent.

As a part of the configuration upgrade we may drop unused Terraform components.

[Grigory]

It is blocked now, see terraform-aws-modules/terraform-aws-eks#1744

[Grigory]

I'll keep it open hanging in a debt! Since we'll have to finish it later (hopefully).

[Grigory]

#222 (this issue should probably live in another repo now)

[jpolchlo]

Note that we have a new deployment that supersedes the one in this repo here.