Fix controllers to use Post/Redirect/Get

Forms should use Post/Redirect/Get pattern.

spring-boot-modules/spring-boot-crud/src/main/java/com/baeldung/crud/controllers/UserController.java

@@ -36,7 +36,7 @@ public class UserController {
         
         userRepository.save(user);
         model.addAttribute("users", userRepository.findAll());
-        return "index";
+        return "redirect:/index";
     }
     
     @GetMapping("/edit/{id}")
@@ -55,7 +55,7 @@ public class UserController {
         
         userRepository.save(user);
         model.addAttribute("users", userRepository.findAll());
-        return "index";
+        return "redirect:/index";
     }
     
     @GetMapping("/delete/{id}")