Add support for diskType to NodeGroup and ManagedNodeGroup

[Kurounin]

Affected feature

When creating a new NodeGroup or ManagedNodeGroup using createManagedNodeGroup there's no option to set the diskType (as seen here https://registry.terraform.io/modules/terraform-aws-modules/eks/aws/latest/submodules/node_groups). By adding the option I would like to start using gp3 volumes instead of gp2 for node instances.

[gcaride]

Yes! We need this, since we can select the amount of throughput and IOPS

[tma-unwire]

This would be really nice as it wil speed up my cluster significantly.

[roothorp]

This feature has been present for a while, but the issue wasn't closed. Fixed in #641.