fix: escape emptyDir braces in f-string to prevent SyntaxError

The config-generated emptyDir volume added inside an f-string
used literal {} which Python interprets as an empty expression.
Escaped to {{}} so it renders as {} in the generated script.

Made-with: Cursor

backend/routers/clusters.py

@@ -1612,7 +1612,7 @@ spec:
           name: inspektor-gadget-config
           defaultMode: 0400
       - name: config-generated
-        emptyDir: {}
+        emptyDir: {{}}
       # Persistent storage for WASM cache
       - name: wasm-cache
         ephemeral: