Add SSM var to optionally disable its use

[jjti]

In our E2E tests, we can hit errors where the GH role does not have auth to make IAM roles. This adds an optional arg for whether to use SSM in the test.

Testing

E2E tested with settings below. HashiCups spun up, did not have SSM:

locals {
  vpc_region       = "us-east-1"
  hvn_region       = "us-east-1"
  cluster_id       = "hc-ec2-cluster"
  hvn_id           = "hc-ec2-cluster-hvn"
  install_demo_app = true
  ssh              = true
  ssm              = false
}