How to get a fancy FilteredSelectMultiple many-to-many admin field in Django

admin.py

from django import forms
from django.contrib import admin
from django.contrib.admin import widgets

class GroupAdminForm(forms.ModelForm):
    users = forms.ModelMultipleChoiceField(
        queryset=models.User.objects.all().order_by("username"),
        required=False,
        # Use the pretty 'filter_horizontal widget'.
        widget=widgets.RelatedFieldWidgetWrapper(
            widgets.FilteredSelectMultiple("users", False),
            models.UserGroup._meta.get_field("user"),
            admin.site,
            # Avoid problem where it tries to resolve auth_group_add, even though in our case it's auth_usergroup_add
            can_add_related=False,
        ),
        label="Users",
    )

    tenants = forms.ModelMultipleChoiceField(
        queryset=models.Tenant.objects.all(),
        required=False,
        # Use the pretty 'filter_horizontal widget'.
        widget=widgets.RelatedFieldWidgetWrapper(
            widgets.FilteredSelectMultiple("tenants", False),
            models.UserGroup._meta.get_field("tenants").remote_field,
            admin.site,
        ),
        label="Tenants",
    )

    def __init__(self, *args, **kwargs):
        # Do the normal form initialisation.
        super().__init__(*args, **kwargs)
        # If it is an existing group (saved objects have a pk).
        if self.instance.pk:
            # Populate the users field with the current Group users.
            self.fields["users"].initial = self.instance.user_set.all()

    def save_m2m(self):
        self.instance.user_set.set(self.cleaned_data["users"])

    def save(self, *args, **kwargs):
        # Default save
        instance = super().save()
        # Save many-to-many data
        self.save_m2m()
        return instance

    class Meta:
        model = models.UserGroup
        fields = "__all__"


@admin.register(models.UserGroup)
class GroupAdmin(DjangoGroupAdmin):
    form = GroupAdminForm