#63 feat: adding rocket chat config

gemeinsamforschen/src/main/java/unipotsdam/gf/config/GFRocketChatConfig.java

+package unipotsdam.gf.config;
+
+public class GFRocketChatConfig {
+
+    public static final String ROCKET_CHAT_LINK = "https://rocket.farm.uni-potsdam.de/";
+    public static final String ADMIN_USERNAME = "";
+    public static final String ADMIN_PASSWORD = "";
+}