Front : create class to connect, send and receive message

- Create environment class
 - Create Connexion class to connect and save data
 - Refactor back api

front/src/Enum/EnvironmentVariable.ts

@@ -0,0 +1,5 @@
+const API_URL = process.env.API_URL || "http://api.workadventure.localhost";
+
+export {
+    API_URL
+}