Multiple firmwares in a single ROS2 workspace

Hey,

at the moment I build some custom firmware with the commands:
```
ros2 run micro_ros_setup create_firmware_ws.sh zephyr nucleo_f446re
ros2 run micro_ros_setup configure_firmware.sh foxtech_eh2000 --transport serial
ros2 run micro_ros_setup build_firmware.sh
```

So we have the simple structure:

```
./firmware/APP
./firmware/PLATFORM
./firmware/TRANSPORT
./firmware/build/zephyr/zephyr.elf
./firmware/zephyr_apps/apps/foxtech_eh2000
...
```

However, this does not allow to create multiple firmwares, where each firmware could be built with a different OS/board/transport/app.

I would prefer a structure like this:
```
ros2 run micro_ros_setup create_firmware_ws.sh
ros2 run micro_ros_setup create_firmware.sh eh2000 --os zephyr --board nucleo_f446re
ros2 run micro_ros_setup configure_firmware.sh eh2000 --app foxtech_eh2000 --transport serial
ros2 run micro_ros_setup build_firmware.sh eh2000
ros2 run micro_ros_setup flash_firmware.sh eh2000

ros2 run micro_ros_setup create_firmware.sh second_firmware --os zephyr --board nucleo_f401rc
ros2 run micro_ros_setup configure_firmware.sh second_firmware --app ping_pong --transport serial
ros2 run micro_ros_setup build_firmware.sh second_firmware
ros2 run micro_ros_setup flash_firmware.sh second_firmware
```

->

```
./firmware/firmwares/eh2000/APP
./firmware/firmwares/eh2000/PLATFORM
./firmware/firmwares/eh2000/TRANSPORT
./firmware/firmwares/eh2000/build/zephyr/zephyr.elf
./firmware/firmwares/second_firmware/APP
./firmware/firmwares/second_firmware/PLATFORM
./firmware/firmwares/second_firmware/TRANSPORT
./firmware/firmwares/second_firmware/build/zephyr/zephyr.elf
./firmware/zephyr_apps/apps/foxtech_eh2000
./firmware/zephyr_apps/apps/ping_pong
```

Is that a sane request? Do you have other ideas?

Cheers
David

既存の create_firmware_ws.sh、configure_firmware.sh、build_firmware.sh、flash_firmware.sh のエントリーポイントと、現在の firmware ディレクトリ構成を確認します。名前付き firmware が OS、board、transport、app、build、flash の設定を個別に保持できる方法を定義します。2 つのサンプル firmware が共存し、それぞれ独立してビルドできるようになれば作業完了です。

索引モデルが issue の本文から書いたものです。