Add selectors to frontend services (#49701)

Co-authored-by: Franck Nijhof <git@frenck.dev>

homeassistant/components/frontend/services.yaml

@@ -1,14 +1,26 @@
 # Describes the format for available frontend services
 
 set_theme:
+  name: Set theme
   description: Set a theme unless the client selected per-device theme.
   fields:
     name:
+      name: Name
       description: Name of a predefined theme, 'default' or 'none'.
+      required: true
       example: "default"
+      selector:
+        text:
     mode:
-      description: The mode the theme is for, either 'dark' or 'light' (default).
+      name: Mode
+      description: The mode the theme is for, either 'dark' or 'light'.
+      default: "light"
       example: "dark"
+      selector:
+        options:
+          - "dark"
+          - "light"
 
 reload_themes:
+  name: Reload themes
   description: Reload themes from YAML configuration.