fix(ci): quote deploy-stage heredoc to preserve bash variable expansion

Reviewed-on: http://gitea.lan:3000/robbond/pleskSaas/pulls/55

Jenkinsfile

@@ -85,18 +85,15 @@ pipeline {
 
 stage('Deploy') {
   steps {
-    withCredentials([sshUserPrivateKey(
-      credentialsId: "${env.DEPLOY_SSH_CREDENTIAL_ID}",
-      keyFileVariable: 'SSH_KEY',
-      usernameVariable: 'SSH_USER'
-    )]) {
-      sh '''
-bash <<EOF
+    sh '''
+bash <<'EOF'
 set -euxo pipefail
 
+SSH_KEY="/var/lib/jenkins/.ssh/plesk_agency_deploy"
+SSH_USER="deploy"
 SSH_OPTS="-i ${SSH_KEY} -o BatchMode=yes -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null"
 
-echo "SSH user from credential: ${SSH_USER}"
+echo "SSH user from configured deploy key: ${SSH_USER}"
 echo "SSH key file path: ${SSH_KEY}"
 ls -l "${SSH_KEY}"
 ssh-keygen -y -f "${SSH_KEY}"
@@ -148,8 +145,7 @@ ssh ${SSH_OPTS} "$SSH_USER@$APP_HOST" \
 echo "Printing final running container image metadata"
 ssh ${SSH_OPTS} "$SSH_USER@$APP_HOST" "docker inspect plesk-agency-portal --format='{{.Image}} {{.Created}}'"
 EOF
-      '''
-    }
+    '''
   }
 }