feat(admin): a password an administrator sets can be one the user must change

The administrator's password form has "The user must change it at their
next login". With it, the user is sent to the change form until they
choose their own, as the generated admin password already does.

admin/forms.py

@@ -1,5 +1,6 @@
 from django import forms
 from django.contrib.auth import password_validation
+from django.contrib.auth.forms import AdminPasswordChangeForm
 from django.contrib.auth.models import Group, User
 from django.core.exceptions import ValidationError
 from django.utils.translation import gettext_lazy as _
@@ -123,3 +124,12 @@ class UserAttributesForm(forms.ModelForm):
     class Meta:
         model = UserAttributes
         exclude = ["user", "can_clone_instances", "must_change_password"]
+
+
+class AdminPasswordForm(AdminPasswordChangeForm):
+    """A password an administrator sets; the user may have to change it at their next login."""
+    must_change_password = forms.BooleanField(label=_("The user must change it at their next login"), required=False)
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.fields["must_change_password"] = self.fields.pop("must_change_password")  # last, after Django's own