[ADD] sentinel user and migrate fleetactivitytracking

allianceauth/framework/api/user.py

@@ -0,0 +1,15 @@
+"""
+Alliance Auth User API
+"""
+
+from django.contrib.auth.models import User
+
+
+def get_sentinel_user() -> User:
+    """
+    Get the sentinel user or create one
+
+    :return:
+    """
+
+    return User.objects.get_or_create(username="deleted")[0]