Add High Availability Support

[faem]

General:

• Have you removed all sensitive information, including but not limited to access keys and passwords?
• Have you checked to ensure there aren't other open or closed pull requests for the same bug/feature/question?
• Have you followed our pull request guidelines?

[faem]

Sample cluster.tf

variable "server_type_node" {
  default = "g6-standard-2"
}
variable "nodes" {
  default = 1
}
variable "server_type_master" {
  default = "g6-standard-2"
}
variable "region" {
  default = "eu-west"
}
variable "ssh_public_key" {
  default = "/home/fahim/.ssh/id_rsa.pub"
}
module "k8s" {
  source  = "git::https://github.com/faem/terraform-linode-k8s.git?ref=add-multi-master"
  #source  = "../../terraform-linode-k8s" 
  k8s_version = "v1.14.0"
  linode_token = "LINODE_TOKEN"
  server_type_node = "${var.server_type_node}"
  addl-masters = "2"
  nodes = "${var.nodes}"
  server_type_master = "${var.server_type_master}"
  region = "${var.region}"
  ssh_public_key = "${var.ssh_public_key}"
}