Parameterize IaaS resources in PVC ECS on IaaS example

[wmudge]

a few notes on this example: Can we avoid hardcoding instance type, instance counts, disk sizes/types and ami types inside the terraform config files? Would like to have the option parameterize those values and pass in from definition.yml

Originally posted by @clevesque in https://github.com/cloudera-labs/cloudera-deploy/issues/143#issuecomment-2150616941