fix(exp_modem): DTE should own both command and data terminal

reworks to clear shared_ptr<> of both command and data terminals
and having DTE own it. When we swith to CMUX mode the ownership is transfered to CMux terminal

components/esp_modem/examples/modem_console/main/console_helper.hpp

@@ -10,6 +10,7 @@
 #pragma once
 
 #include <vector>
+#include <string>
 #include <algorithm>
 #include <functional>
 #include <esp_console.h>