feat: add RadioSettings fixture

fixtures/sample/radiosettings.json

+[
+  {
+    "model": "program.radiosettings",
+    "pk": 1,
+    "fields": {
+      "cba_api_key": "dea",
+      "cba_domains": [
+        "cba.media"
+      ],
+      "fallback_show": null,
+      "line_in_channels": {
+        "1": "live",
+        "2": "preprod"
+      },
+      "station_logo": null,
+      "station_name": "Radio Helsinki",
+      "station_website": "https://helsinki.at/"
+    }
+  }
+]