Add power command to System Bridge docs (#28037)

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

source/_integrations/system_bridge.markdown

@@ -137,3 +137,26 @@ data:
   bridge: "deviceid"
   text: "Hello"
 ```
+
+### Service `system_bridge.power_command`
+
+Sends power command to the system.
+
+{% my developer_call_service service="system_bridge.power_command" title="Show service in your Home Assistant instance." %}
+
+
+```yaml
+service: system_bridge.power_command
+data:
+  bridge: "device"
+  command: "sleep"
+```
+
+Supported commands are:
+
+- `hibernate`
+- `lock`
+- `logout`
+- `restart`
+- `shutdown`
+- `sleep`