Remove server settings from the session cookie

[axelstudios]

Any background context you want to provide?

The sessionid cookie should have only the minimal session-specific data necessary, and not server settings that can become out-of-sync if stored in session tokens

What's this PR do?

Overrides the two_factor.views.core.LoginView.render method to make the backend setting INCLUDE_ACCT_REG available to the view template without storing it in each user's session cookie

How should this be manually tested?

1. In local_untracked.py toggle the INCLUDE_ACCT_REG = True variable and check that the login page correctly renders (or hides) the Create my Account button

2. Optionally inspect the session cookie data and ensure the include_acct_reg is no longer included. Copy your sessionid cookie value and run the following commands:

   # shell
   export DJANGO_SETTINGS_MODULE="config.settings.local_untracked"

   # python
   from django.conf import settings
   from django.core import signing
   
   cookie_value = "YOUR_SESSIONID_COOKIE_VALUE"
   
   decoded = signing.loads(
       cookie_value,
       key=settings.SECRET_KEY,
       salt="django.contrib.sessions.backends.signed_cookies",
   )
   
   print(decoded)

   The new session data (for a logged-out user) should show the following:

   {
     "wizard_custom_login_view": {
       "step": "auth",
       "step_data": {},
       "step_files": {},
       "extra_data": {},
       "validated_step_data": {}
     }
   }

[perryr16]

Works great 🏆