feat: Replace the local-exec script with a http datasource for waiting cluster (#1339)

NOTES: Using the [terraform-aws-modules/http](https://registry.terraform.io/providers/terraform-aws-modules/http/latest) provider is a more platform agnostic way to wait for the cluster availability than using a local-exec. With this change we're able to provision EKS clusters and manage the `aws_auth` configmap while still using the `hashicorp/tfc-agent` docker image.

variables.tf

@@ -205,18 +205,6 @@ variable "cluster_delete_timeout" {
   default     = "15m"
 }
 
-variable "wait_for_cluster_cmd" {
-  description = "Custom local-exec command to execute for determining if the eks cluster is healthy. Cluster endpoint will be available as an environment variable called ENDPOINT"
-  type        = string
-  default     = "for i in `seq 1 60`; do if `command -v wget > /dev/null`; then wget --no-check-certificate -O - -q $ENDPOINT/healthz >/dev/null && exit 0 || true; else curl -k -s $ENDPOINT/healthz >/dev/null && exit 0 || true;fi; sleep 5; done; echo TIMEOUT && exit 1"
-}
-
-variable "wait_for_cluster_interpreter" {
-  description = "Custom local-exec command line interpreter for the command to determining if the eks cluster is healthy."
-  type        = list(string)
-  default     = ["/bin/sh", "-c"]
-}
-
 variable "cluster_create_security_group" {
   description = "Whether to create a security group for the cluster or attach the cluster to `cluster_security_group_id`."
   type        = bool