add potential deprecation warning for email_relay.db.EmailDatabaseRouter

src/email_relay/checks.py

@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+from django.conf import settings
+from django.core.checks import Tags
+from django.core.checks import Warning
+from django.core.checks import register
+
+from email_relay.db import EmailDatabaseRouter
+
+
+@register(Tags.compatibility)
+def check_for_deprecated_db_router(app_configs, **kwargs):
+    if (
+        "email_relay" in settings.INSTALLED_APPS
+        and "email_relay.db.EmailDatabaseRouter" in settings.DATABASE_ROUTERS
+    ):
+        return [
+            Warning(
+                "The email_relay.db.EmailDatabaseRouter will potentially be deprecated in a future version.",
+                hint="Please visit https://github.com/westerveltco/django-email-relay/issues/154 for more information.",
+                obj=EmailDatabaseRouter,
+                id="email_relay.W001",
+            )
+        ]
+    return []