feat(dbus): Add support for configuring the external antenna

Introduce the `configure_external_antenna` function to manage external
antenna settings, including enable, disable, and status checks. Update
the feature configuration in `interface_config` to include this
functionality. This enhances WiFi-related configuration options.

src/revpi_middleware/dbus_middleware1/system_config/interface_config.py

@@ -9,6 +9,7 @@ from .revpi_config import (
     ConfigActions,
     configure_avahi_daemon,
     configure_dphys_swapfile,
+    configure_external_antenna,
     configure_gui,
     simple_systemd,
 )
@@ -92,5 +93,5 @@ AVAILABLE_FEATURES = {
     "bluetooth": False,
     "ieee80211": False,
     "avahi": FeatureFunction(configure_avahi_daemon, []),
-    "external-antenna": False,
+    "external-antenna": FeatureFunction(configure_external_antenna, []),
 }