added file to separate client function from the server

to conform to instructions

app/client.go

+package main
+
+import (
+	. "node/types"
+)
+
+/*
+ * @file
+ * @brief Distributed Systems - Blockchain
+ * @author Xavier Perret
+ * @date 28/09/2022 - 05/10/2022
+ */
+
+func main() {
+
+}