Add Admin template page branch processing according to custom_admin s…

[komo3344]

If you run a project after forking or cloning, you will not be able to access the administrator page.

1. docker-compose up
2. docker-compose run django migrate
3. docker-compose run django createsuperuser
4. access admin page -> X

Because django.contrib.admin is the default setting.

Therefore, the configuration of the administrator page should be different according to the INSTALLED_APP setting.