feat(gateways): Introduce gateway model and update agent provisioning templates

backend/app/models/__init__.py

@@ -1,6 +1,7 @@
 from app.models.activity_events import ActivityEvent
 from app.models.agents import Agent
 from app.models.boards import Board
+from app.models.gateways import Gateway
 from app.models.tasks import Task
 from app.models.users import User
 
@@ -8,6 +9,7 @@ __all__ = [
     "ActivityEvent",
     "Agent",
     "Board",
+    "Gateway",
     "Task",
     "User",
 ]