[change] Added configuration settings for dj-rest-auth >= 3.0

The development version of openwisp-radius increased the dependecy
version of dj-rest-auth.

The dj-rest-auth >= changed configuration settings. This patch
adds those settings without removing the old settings. This is done
to maintain backward compatabilty with older version of dj-rest-auth.

Related to openwisp/openwisp-radius@265f88a

templates/openwisp2/settings.py

@@ -151,12 +151,24 @@
 
 {% if openwisp2_radius %}
 OPENWISP_RADIUS_FREERADIUS_ALLOWED_HOSTS = {{ openwisp2_radius_allowed_hosts }}
+REST_AUTH = {
+    'SESSION_LOGIN': False,
+    'PASSWORD_RESET_SERIALIZER': 'openwisp_radius.api.serializers.PasswordResetSerializer',
+    'REGISTER_SERIALIZER': 'openwisp_radius.api.serializers.RegisterSerializer',
+}
+
+# dj-rest-auth 3.0 changed the configuration settings.
+# The below settings are kept for backward compatability with dj-rest-auth < 3.0
+#
+# Backward compatible settings begins
 REST_AUTH_SERIALIZERS = {
     'PASSWORD_RESET_SERIALIZER': 'openwisp_radius.api.serializers.PasswordResetSerializer',
 }
 REST_AUTH_REGISTER_SERIALIZERS = {
     'REGISTER_SERIALIZER': 'openwisp_radius.api.serializers.RegisterSerializer',
 }
+# Backward compatible settings ends
+
 # SMS settings
 OPENWISP_RADIUS_SMS_TOKEN_MAX_IP_DAILY = {{ openwisp2_radius_sms_token_max_ip_daily }}
 SENDSMS_BACKEND = '{{ openwisp2_radius_sms_backend }}'