build: 后台主页，错误页面跳转

backend/app/src/main/java/io/metersphere/controller/CustomErrorController.java

@@ -0,0 +1,14 @@
+package io.metersphere.controller;
+
+import org.springframework.boot.web.servlet.error.ErrorController;
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.GetMapping;
+
+@Controller
+public class CustomErrorController implements ErrorController {
+
+    @GetMapping("/error")
+    public String redirectRoot() {
+        return "redirect:/";
+    }
+}

backend/app/src/main/java/io/metersphere/controller/IndexController.java

@@ -0,0 +1,12 @@
+package io.metersphere.controller;
+
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.GetMapping;
+
+@Controller
+public class IndexController {
+    @GetMapping("/")
+    public String index() {
+        return "index.html";
+    }
+}