🔥(backend) remove all code related to template

The template feature is removed.
Migration created to drop related tables.
Files modified:
- viewsets
- serializers
- models
- admin
- factories
- urls
- tests
- demo data

src/backend/impress/settings.py

@@ -406,16 +406,6 @@ class Base(Configuration):
                 environ_name="API_DOCUMENT_ACCESS_THROTTLE_RATE",
                 environ_prefix=None,
             ),
-            "template": values.Value(
-                default="30/minute",
-                environ_name="API_TEMPLATE_THROTTLE_RATE",
-                environ_prefix=None,
-            ),
-            "template_access": values.Value(
-                default="30/minute",
-                environ_name="API_TEMPLATE_ACCESS_THROTTLE_RATE",
-                environ_prefix=None,
-            ),
             "invitation": values.Value(
                 default="60/minute",
                 environ_name="API_INVITATION_THROTTLE_RATE",