feat: Integrate VND7050AJ driver and enhance gateway settings

This commit introduces the VND7050AJ driver as a new submodule and integrates it into the project.

Key changes include:
- Added  as a git submodule.
- Enhanced the gateway application () with LittleFS and the settings subsystem.
  - Implemented new shell commands (, , ) for managing custom settings.
  - Added functionality to compact the settings file.
- Updated  to include new library dependencies and log  return code.
- Adjusted include paths for  in relevant files.
Signed-off-by: Eduard Iten <eduard@iten.pro>

software/apps/slave_node/src/main.c

@@ -9,6 +9,7 @@ LOG_MODULE_REGISTER(main, LOG_LEVEL_INF);
 
 int main(void)
 {
+	int rc;
 	LOG_INF("Starting Irrigation System Slave Node");
 
 	if (settings_subsys_init() || settings_load()) {
@@ -18,9 +19,10 @@ int main(void)
 	valve_init();
 	fwu_init();
 
-	if (modbus_server_init()) {
-		LOG_ERR("Modbus RTU server initialization failed");
-		return 0;
+	rc = modbus_server_init();
+	if (rc) {
+		LOG_ERR("Modbus server initialization failed: %d", rc);
+		return rc;
 	}
 
 	LOG_INF("Irrigation System Slave Node started successfully");