add controller, index.html, admin in application.properties

src/main/java/mops/gruppen2/controllers/Gruppen2Controller.java

@@ -0,0 +1,12 @@
+package mops.gruppen2.controllers;
+
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.GetMapping;
+
+@Controller
+public class Gruppen2Controller {
+    @GetMapping("/")
+    public String index() {
+        return "index";
+    }
+}