Add Jenkins pipeline for building and pushing Docker image

Signed-off-by: Riz Urian <98958099+rizjosel@users.noreply.github.com>

Jenkinsfile

@@ -0,0 +1,45 @@
+pipeline {
+    triggers {
+        githubPush()
+    }
+    agent any
+    environment {
+        APP_NAME    = "petclinic"
+        DOCKER_USER = "rizjosel"
+        IMAGE_TAG   = "${BUILD_NUMBER}"
+        IMAGE_NAME  = "${DOCKER_USER}/${APP_NAME}:${IMAGE_TAG}"
+    }
+    stages {
+
+        stage('List Workspace') {
+            steps {
+                sh 'ls -l'
+            }
+        }
+
+        stage('Build Application (Gradle)') {
+            steps {
+                sh './gradlew clean build -x test'
+                archiveArtifacts artifacts: 'build/libs/*.jar', fingerprint: true
+            }
+        }
+
+        stage('Build Docker Image') {
+            steps {
+                sh "docker build -t ${IMAGE_NAME} ."
+            }
+        }
+
+        stage('Docker Push') {
+            steps {
+                withCredentials([string(credentialsId: 'dockerhub-creds', variable: 'DOCKER_TOKEN')]) {
+                    sh """
+                        echo \$DOCKER_TOKEN | docker login -u ${DOCKER_USER} --password-stdin
+                        docker push ${IMAGE_NAME}
+                        docker logout
+                    """
+                }
+            }
+        }
+    }
+}