fix: update fallback_default_pools & add fallback_pools

fixtures/sample/radiosettings.json

@@ -7,7 +7,10 @@
       "cba_domains": [
         "cba.media"
       ],
-      "fallback_default_pool": "",
+      "fallback_default_pool": "fallback",
+      "fallback_pools": {
+        "fallback": "Station Fallback Pool"
+      },
       "fallback_show": null,
       "host_image_aspect_ratio": "1:1",
       "host_image_shape": "round",