feat(ui): remove isRefinerAvailable state, update refiner node

We can derive `isRefinerAvailable` from the query result (eg are there any refiner models installed). This is a piece of server state, so by using the list models response directly, we can avoid needing to manually keep the client in sync with the server.

Created a `useIsRefinerAvailable()` hook to return this boolean wherever it is needed.

Also updated the main models & refiner models endpoints to only return the appropriate models. Now we don't need to filter the data on these endpoints.

invokeai/app/invocations/sdxl.py

@@ -138,7 +138,7 @@ class SDXLRefinerModelLoaderInvocation(BaseInvocation):
             "ui": {
                 "title": "SDXL Refiner Model Loader",
                 "tags": ["model", "loader", "sdxl_refiner"],
-                "type_hints": {"model": "model"},
+                "type_hints": {"model": "refiner_model"},
             },
         }