Add user registration endpoint and HDFS directory creation

- Implemented a new registration endpoint in AuthController to handle user sign-ups.
- Integrated AuthenticationService to save the user and create a corresponding HDFS directory for the user upon registration.
- Updated User entity to return the username instead of email in getUsername method.

src/main/java/com/skycrate/backend/skycrateBackend/services/AuthenticationService.java

@@ -1,10 +1,13 @@
 package com.skycrate.backend.skycrateBackend.services;
 
+import com.skycrate.backend.skycrateBackend.config.HDFSConfig;
 import com.skycrate.backend.skycrateBackend.dto.LoginUserDto;
 import com.skycrate.backend.skycrateBackend.dto.RegisterUserDto;
 import com.skycrate.backend.skycrateBackend.entity.User;
 import com.skycrate.backend.skycrateBackend.repository.UserRepository;
 import com.skycrate.backend.skycrateBackend.utils.RSAKeyUtil;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
 import org.springframework.security.authentication.AuthenticationManager;
 import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
 import org.springframework.security.crypto.password.PasswordEncoder;
@@ -45,7 +48,20 @@ public class AuthenticationService {
                 .privateKey(keyPair.getPrivate().getEncoded())
                 .build();
 
-        return userRepository.save(user);
+        User savedUser = userRepository.save(user);
+
+        // Create HDFS directory in root with username
+        try {
+            FileSystem fs = HDFSConfig.getHDFS();
+            String folderName = savedUser.getUsername();
+            Path userDir = new Path("/" + folderName);
+            if (!fs.exists(userDir)) {
+                fs.mkdirs(userDir);
+            }
+        } catch (Exception e) {
+            throw new RuntimeException("Failed to create HDFS directory for user: " + savedUser.getUsername(), e);
+        }
+        return savedUser;
     }
 
     public User authenticate(LoginUserDto inputUser) {