Demo similar to multithread_publisher_subscriber from rclc but in Zephyr. Multithreading not working as espected.

還沒有人認領這個 Issue。

## Issue template

- Hardware description: Olimex STM32-E407
- RTOS: Zephyr
- Installation type: -
- Version or commit hash: -

#### Steps to reproduce the issue
Install Micro-Ros like in the Tutorial: [Tutorial Micro-ROS and Zephyr](https://micro.ros.org/docs/tutorials/core/first_application_rtos/zephyr/)

Then add this App from this Repository: [Micro-ROS and Zephyr](https://github.com/Johannes-42/microROS_Zephyr-)
If that is run It will publish 2 numbers from 2 threads. The main thread and the second created thread.
But if the publisher in the main thread is commented out. Also, the second thread will not publish anymore.
Is that wanted behavior or am I doing something wrong?

#### Expected behavior
Multithreaded Threads can publish their publishers

#### Actual behavior
Multithreaded Threads only publish if the main thread is publishing.

#### Additional information
I also tried it with a timer, then the second thread will publish only if the timer is used and in the same time interval.

I want to use Micro-ROS multithreaded to give some threads a higher priority than others. One more question to that would be if it is possible to start multiple apps in Zephyr? something like:
ros2 run micro_ros_setup configure_firmware.sh ping_pong ping_pong2 --transport serial-usb
This command would not work but is there a way to run 2 apps?

從 Zephyr 教學和所引用的 Micro-ROS 與 Zephyr 應用程式開始，然後將其雙執行緒 publisher 設定與 rclc multithread_publisher_subscriber 示範進行比較。在 Olimex STM32-E407 上重現該行為，並判斷是否支援獨立執行緒發布以及執行多個 app；記錄已確認的行為以及所需的變更或限制。

由索引模型根據 Issue 內容生成。