title: Terraform ConfigMap hash for redeploy
body: <p>I am using Terraform with Kubernetes Provider.
  Now when creating <em>ConfigMap</em>s, I want their names to have a content suffix. 
  Usually it is a hash of the content.</p>
  
  <p>This way, it should enforce a Deployment, where used.</p>
  
  <p>So I would like it to work similar to:</p>
  
  <pre><code>resource "kubernetes_config_map" "prometheus_config" {
    metadata {
      name      = "prometheus-" + computeHash(file("${path.module}/alerts.yml"), file("${path.module}/recordings.yml"), "abcd")
    }
  
    data = {
      "foo" = file("${path.module}/alerts.yml")
      "bar" = file("${path.module}/recordings.yml")
      "txt" = "abcd"
    }
  }
  </code></pre>
  
  <p>Is there any way of implementing a custom function like <code>computeHash</code>?
  Or to achieve this another way?</p>