Initial implementation of custom price triggers

- likely to have some bugs, but this is good enough for a preview release.

token_bot/controller/alerts.py

@@ -41,3 +41,18 @@ class AlertsController:
         alert = self._alert_to_obj(alert)
         user = self._user_to_obj(user)
         await alert.remove_user(self.table, user)
+
+    async def get_all_by_type(self, alert_type: int) -> List[Alert]:
+        """Query all alerts of a specific type from the database."""
+        from aiodynamo.expressions import F
+        alerts = []
+        async for item in self.table.query(
+            key_condition=F("alert").equals(alert_type)
+        ):
+            alert = Alert.from_item(
+                primary_key=item["alert"],
+                sort_key=item["flavor-region-price"],
+                users=item.get("users", [])
+            )
+            alerts.append(alert)
+        return alerts