fix(modbus_server): Implement hardcoded firmware version 0.0.1

Set firmware version to 0.0.1 in modbus_server.c for Modbus tool display.
This is a temporary solution until MCUboot integration is complete.

software/modules/modbus_server/src/modbus_server.c

@@ -1,3 +1,12 @@
+#include <zephyr/kernel.h>
+#include <zephyr/drivers/uart.h>
+#include <zephyr/device.h>
+#include <zephyr/modbus/modbus.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/settings/settings.h>
+#include <zephyr/sys/reboot.h>
+#include "modbus_server.h"
+#include "valve.h"
 #include "fwu.h"
 
 #include <zephyr/usb/usb_device.h>