The modbus register documentation in `docs/modbus-registers.de.md` has been updated to be consistent with the implementation in `software/include/lib/modbus_server.h`.
- Register names in the documentation now match the programmatic names in the header file.
- Missing registers `REG_HOLDING_OBSTACLE_THRESHOLD_OPEN_MA` and `REG_HOLDING_OBSTACLE_THRESHOLD_CLOSE_MA` have been added to the documentation.
Signed-off-by: Eduard Iten <eduard@iten.pro>