main : add --in-suffix option (#1318)

* adding --in-suffix option

* print input suffix before generation

examples/common.h

@@ -43,6 +43,7 @@ struct gpt_params {
     std::string prompt = "";
     std::string path_session = "";       // path to file for saving/loading model eval state
     std::string input_prefix = "";       // string to prefix user inputs with
+    std::string input_suffix = "";       // string to suffix user inputs with
     std::vector<std::string> antiprompt; // string upon seeing which more user input is prompted
 
     std::string lora_adapter = "";  // lora adapter path