feat(accounts): failed logins lock a user for the address they come from

Nothing limited failed logins: a password could be guessed at the speed
the server answers. django-axes (8.3.1, Django 5.2, Python 3.10-3.13)
now counts them.

- A user is locked for the address the failed logins come from
  (username and IP together), so an attacker cannot lock someone out
  from elsewhere and users behind one NAT address do not share a lock.
  A successful login resets the count. axes sits in front of every
  authentication: the login page with or without OTP, LDAP and the API.
- The number of failed logins (default 5) and the lock time in minutes
  (default 15) are on the Settings page (LOGIN_FAILURE_LIMIT,
  LOGIN_LOCKOUT_MINUTES, added by migration appsettings.0014) and apply
  at once; an invalid value falls back to the default. Unlock with
  "manage.py axes_reset_username <username>".
- Behind the bundled nginx every request comes from 127.0.0.1; the
  client address is read from X-Real-IP, which nginx sets, but only for
  requests from a loopback address or from LOGIN_TRUSTED_PROXIES, so a
  forged header does not escape a lock.

settings.py.template gets the app, middleware, backend and AXES_*
settings; README tells existing installations what to copy. Tests that
call client.login now pass a request, which the axes backend needs.
The new tests fail with axes disabled.

admin/tests.py

@@ -1,14 +1,14 @@
 from django.contrib.auth.models import Group, User
 from django.core.exceptions import ObjectDoesNotExist
 from django.shortcuts import reverse
-from django.test import TestCase
+from django.test import RequestFactory, TestCase
 
 from accounts.models import UserAttributes
 
 
 class AdminTestCase(TestCase):
     def setUp(self):
-        self.client.login(username="admin", password="admin")
+        self.client.login(request=RequestFactory().get("/"), username="admin", password="admin")
 
     def test_group_list(self):
         response = self.client.get(reverse("admin:group_list"))