Support building STM32-based projects on Github

[pamolloy]

See Build Guide for STM32 Platform.

For now the only example we have is using an STM32 Nucleo standard board. New projects will have to setup a whole new ST32CubeMX pin mapping.

[RICCIARDI-Adrien]

Here is the beginning of a GitHub action : it successfully installs the Cube MX and Cube IDE tools (there is also a GitHub action that provides the Cube IDE tool). https://github.com/RICCIARDI-Adrien/precision-converters-firmware/tree/adrien/add_stm32_ci_support

[pamolloy]

https://www.st.com/en/development-tools/stm32cubeclt.html?rt=um&id=UM3088