Add antispam app

* update_spam_database command to update suspicious domains from an
   external provider
* Add a AntiSpamEmailField that deny emails from suspicious domains
* Update documentation

antispam/migrations/0001_initial.py

@@ -0,0 +1,35 @@
+# Generated by Django 4.2.14 on 2024-08-03 23:05
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="ToxicDomain",
+            fields=[
+                (
+                    "domain",
+                    models.URLField(
+                        max_length=253,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="domain",
+                    ),
+                ),
+                ("created", models.DateTimeField(auto_now_add=True)),
+                (
+                    "is_externally_managed",
+                    models.BooleanField(
+                        default=False,
+                        help_text="True if kept up-to-date using external toxic domain providers, else False",
+                        verbose_name="is externally managed",
+                    ),
+                ),
+            ],
+        ),
+    ]