Update credentials handling in Gradle and Jenkinsfile for improved security

Jenkinsfile

@@ -3,7 +3,12 @@ pipeline {
     stages {
         stage('Gradle') {
             steps {
-                sh './gradlew build'
+                withCredentials([usernamePassword(credentialsId: 'destro-repo-user', usernameVariable: 'USERNAME', passwordVariable: 'PASSWORD')]) {
+                    sh '''
+                        chmod +x gradlew
+                        ./gradlew build -PalttdDevPublishUser=$USERNAME -PalttdDevPublishPass=$PASSWORD
+                    '''
+                }
             }
         }
         stage('Archive') {
@@ -17,4 +22,4 @@ pipeline {
             }
         }
     }
-}
+}