Add missing destroy function.

The component allocates resources (timers, event loop) in relay_chn_create but never frees them. This is a resource leak.
Hence, a destroy function added to free the resources gracefully.

Fixes #1048.

include/relay_chn.h

@@ -97,6 +97,13 @@ typedef void (*relay_chn_state_listener_t)(uint8_t chn_id, relay_chn_state_t old
  */
 esp_err_t relay_chn_create(const gpio_num_t* gpio_map, uint8_t gpio_count);
 
+/**
+ * @brief Destroy the relay channels and free resources.
+ *
+ * This function cleans up the relay channels and releases any resources allocated during their creation.
+ */
+void relay_chn_destroy(void);
+
 /**
  * @brief Register a channel state change listener.
  *