add: поле updated_at (Дата обновления) в модели +миграции, админке, блогах, страницах и sitemaps.xml

etpgrf_site/blog/templates/blog/page_detail.html

@@ -23,7 +23,7 @@
      }
    },
    "datePublished": "{{ page.published_at|date:'Y-m-d' }}",
-   "dateModified": "{{ page.published_at|date:'Y-m-d' }}"
+   "dateModified": "{{ page.updated_at|date:'Y-m-d' }}"
  }
    </script>{% endblock %}
 

etpgrf_site/blog/templates/blog/post_detail.html

@@ -27,7 +27,7 @@
     }
   },
   "datePublished": "{{ post.published_at|date:'Y-m-d' }}",
-  "dateModified": "{{ post.published_at|date:'Y-m-d' }}"
+  "dateModified": "{{ post.updated_at|date:'Y-m-d' }}"
 }
   </script>{% endblock %}