feat: add helm upgrade CD pipeline for rest api

fixes issue #40

Jenkinsfile

@@ -3,6 +3,15 @@ pipeline {
   tools { nodejs "node" }
   environment {
     GH_TOKEN = credentials('jenkins-pat')
+    SSH_CREDENTIAL_ID = credentials('gke-bastion') // bastion sshagent
+    BASTION_IP = credentials('bastion-ip') // bastion host ip address
+    USERNAME = credentials('bastion-username') // bastion host username
+    PRIVATE_KEY = credentials('private-key') // ssh key for bastion
+    K8S_SA_JSON = credentials('k8s-sa-json') // json file for K8S SA
+    ROBOCOP = credentials('robocop') // image pull secrets for quay.io
+    GKE_CLUSTER_NAME = credentials('gke-cluster-name') // cluster name
+    GKE_CLUSTER_REGION = credentials('gke-cluster-region') // cluster region
+    GKE_PROJECT_NAME = credentials('gke-project-name') // GKE project name
   }
   stages {
     stage('Clone repository') {
@@ -44,6 +53,31 @@ pipeline {
         }
       }
     }
+    stage('Helm Upgrade @ GKE') {
+      when {
+        branch 'master'
+      }
+      steps {
+        sshagent(['gke-bastion']) {
+          sh '''
+          cat $PRIVATE_KEY > gke_compute
+          cat $K8S_SA_JSON > sa.json
+          scp -i gke_compute sa.json $USERNAME@$BASTION_IP:/home/$USERNAME
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP ./download-tarball.sh webapp-helm-chart
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP gcloud auth activate-service-account --key-file=sa.json
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP gcloud config configurations list
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP gcloud container clusters get-credentials $GKE_CLUSTER_NAME --region $GKE_CLUSTER_REGION --project $GKE_PROJECT_NAME
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP kubectl config view
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP kubectl get ns
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP helm ls -n webapp -a
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP mv csye7125-fall2023* webapp-helm-chart
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP helm upgrade -n webapp webapp-helm-release webapp-helm-chart --set=imagePullSecrets.dockerConfig=$ROBOCOP
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP helm ls -n webapp -a
+          ssh -i gke-compute -o StrictHostKeyChecking=no $USERNAME@$BASTION_IP rm -rf webapp-helm-chart*
+          '''
+        }
+      }
+    }
   }
   post {
     always {