How to get a pushover notification when your Heroku app is deployed

heroku.tf

resource "heroku_app" "main" {
  name   = "masutaka-net"
  region = "us"
  stack  = "container"
}

resource "heroku_formation" "web" {
  app      = "${heroku_app.main.name}"
  type     = "web"
  quantity = 1
  size     = "Hobby"
}

variable "pushover_group_key" {
  description = "Pushover Group Key, set Environment Variable $TF_VAR_pushover_group_key"
}

variable "pushover_api_token" {
  description = "Pushover Application API Token, set Environment Variable $TF_VAR_pushover_api_token"
}

locals {
  pushover_parameters = [
    "user=${var.pushover_group_key}",
    "token=${var.pushover_api_token}",
    "device=iPhone",
    "priority=0",
    "title=${urlencode("masutaka.net has deployed")}",
    "message=${urlencode("masutaka deployed app")}",
    "url=${urlencode("https://dashboard.heroku.com/apps/masutaka-net")}",
  ]
}

resource "heroku_addon" "deployhooks" {
  app  = "${heroku_app.main.name}"
  plan = "deployhooks:http"

  config {
    url = "https://api.pushover.net/1/messages.json?${join("&", local.pushover_parameters)}"
  }
}