This commit introduces a major refactoring of the project structure to align
with Zephyr's recommended multi-application and library organization.
Key changes include:
- Relocation of custom modules from 'software/modules/' to 'software/lib/'.
- Introduction of a central 'software/CMakeLists.txt' to manage application
and library subdirectories.
- Creation of new Kconfig files for 'software/' and 'software/apps/slave_node/'
to define project-wide and application-specific configurations.
- Removal of the 'gateway' and 'stm32g431_tests' applications.
- Removal of 'shell_modbus.c' and 'shell_system.c' from 'slave_node' application's
direct source files, indicating a shift towards library-based shell commands.
- Updates to 'software/apps/slave_node/CMakeLists.txt', 'prj.conf', and
'boards/bluepill_f103rb.conf' to reflect the new structure and dependencies.
- Reorganize the software directory to support multiple Zephyr applications (gateway, slave_node).
- Create a clear separation between applications and shared libraries.
- Add placeholder files for gateway and slave_node applications.
Eduard Iten