Add django_ldap_auth

In the ldap.Dockerfile the django_ldap_auth module is installed to
enable authentication againt LDAP servers.

docker/ldap_config.docker.py

@@ -0,0 +1,10 @@
+import importlib.util
+import sys
+
+try:
+  spec = importlib.util.spec_from_file_location('ldap_config', '/etc/netbox/ldap_config.py')
+  module = importlib.util.module_from_spec(spec)
+  spec.loader.exec_module(module)
+  sys.modules['netbox.ldap_config'] = module
+except:
+  raise ImportError('')