docs, examples: use rtc_gpio_isolate to disconnect GPIO12

This is needed to reduce deep sleep current on ESP32-WROVER modules.

Ref TW18165.

examples/system/console/main/cmd_system.c

@@ -113,6 +113,7 @@ static int deep_sleep(int argc, char** argv)
 
         ESP_ERROR_CHECK( esp_sleep_enable_ext1_wakeup(1ULL << io_num, level) );
     }
+    rtc_gpio_isolate(GPIO_NUM_12);
     esp_deep_sleep_start();
 }