feat: change the behavior of destroy warning

[suzuki-shunsuke]

BREAKING CHANGE: change the behavior of destroy warning

---

AS IS

tfcmt posts a deletion warning comment as the other comment.

TO BE

tfcmt posts only one comment whose template is when_destroy.template.

    when_destroy:
      label: "destroy"
      label_color: "d93f0b"  # red
      template: |
        {{ .Title }}
        [CI link]( {{ .Link }} )
        This plan contains **resource deletion**. Please check the plan result very carefully!
        {{ .Message }}
        {{if .Result}}
        <pre><code>{{ .Result }}
        </pre></code>
        {{end}}
        <details><summary>Details (Click me)</summary>
        <pre><code>{{ .Body }}
        </pre></code></details>

And the default title of destroy warning is changed to ## :warning: Resource Deletion will happen :warning:.