Add custom ros message to micro_ros_espidf_component help

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Hi, my project uses micro_ros_espidf_component which works fine with standard int32 messages, but we would like to use a custom message. To be fair I am not an expert in either cmake build system or esp-idf framework.

Our project looks like this:
```
- ourProject/
- CMakeLists.txt
- sdkconfig
- components/
- micro_ros_espidf_component // copy of repo, revision jazzy
- main/
- CMakeLists.txt
- main.c
- idf_component.yml // micro_ros_espidf_component listed as repo dependency
- build/
```
As far as my troubleshooting goes, my attempts to add a `components/msgs` subdirectory have failed and I have since realised that the custom message(s) need to be part of the `micro_ros_espidf_component` itself so they are compiled into `libmicroros.a`.

* My approach is to copy `micro_ros_espidf_component` into a new `components` directory. Then `main/idf_component.yml` lists this as a local directory dependency rather than previously a repo dependency
* the msgs components are not part of `micro_ros_espidf_component` instead `micro_ros_espidf_component/libmicroros.mk` does `git clone https://github.com/micro-ROS/micro_ros_msgs`.
* THE BIG QUESTION What do I need to do here to add a custom message directory which is then picked up and compiled into `libmicroros.a`?
* Ideally I would like to add a MyCustomMessage in a `myrepo/components/msgs/MyCustomMessage.msg` file along the pattern of [this video](https://www.youtube.com/watch?v=E_xBPI8SQig)

Any help is appreciated.

Commencez par libmicroros.mk et les fichiers de composant et main CMakeLists.txt mentionnés dans l’issue ; suivez la manière dont micro_ros_msgs est cloné et dont les packages de messages sont intégrés à libmicroros.a. Reproduisez la configuration locale du composant avec un répertoire .msg personnalisé, documentez ensuite l’organisation de projet prise en charge et vérifiez que le message généré est inclus dans le build ESP-IDF.

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