feat: notify when a user account is deleted (#14113)

coderd/database/migrations/000236_notifications_user_deleted.down.sql

@@ -0,0 +1 @@
+DELETE FROM notification_templates WHERE id = 'f44d9314-ad03-4bc8-95d0-5cad491da6b6';

coderd/database/migrations/000236_notifications_user_deleted.up.sql

@@ -0,0 +1,9 @@
+INSERT INTO notification_templates (id, name, title_template, body_template, "group", actions)
+VALUES ('f44d9314-ad03-4bc8-95d0-5cad491da6b6', 'User account deleted', E'User account "{{.Labels.deleted_account_name}}" deleted',
+        E'Hi {{.UserName}},\n\nUser account **{{.Labels.deleted_account_name}}** has been deleted.',
+        'User Events', '[
+        {
+            "label": "View accounts",
+            "url": "{{ base_url }}/deployment/users?filter=status%3Aactive"
+        }
+    ]'::jsonb);