Add Tags and refactor terraform script

[yash2189]

• Added common_tags for resources and made it reusable.
• Introduced dynamic availability zones

[prabhapa]

We are not creating any IAC code here. But the best implementation would be below (modularising vpc)
structure:

main.tf
vars.tf
vpc_module/
       main.tf    # keep current main.tf code here
       vars.tf    # module inputs**

---

top level vars.tf should have below vars only:

variable "regions_to_be_deployed" {
  description = "List of AWS regions to deploy the VPC"
  type        = list(string)
  default     = ["ap-south-1", "us-east-1"] # these can be chaged as per requirement
}
output "vpc_ids" {
  value = { for region, mod in module.multi_region_vpc : region => mod.vpc_id }
}

top level main.tf should be like it:

module "multi_region_vpc" {
  for_each = toset(var.regions_to_be_deployed)

  source = "./vpc_module"

  aws_region            = each.key
  vpc_cidr              = "10.0.0.0/16"
  vpc_name              = "openshift-sustaining-vpc-${each.key}"
  vpc_owner             = "openshift sustaining slack bot"
  public_subnet_cidr_1  = "10.0.1.0/24"
  public_subnet_cidr_2  = "10.0.2.0/24"
  common_tags           = {
    "app-code"      = "OSUS-002"
    "service-phase" = "dev"
    "cost-center"   = "136"
  }
}

You can try this when you have time..Also add a readme as to how to run this (steps)