Update Jenkins template example for supervisor builder (#375)

builder/vsphere/examples/supervisor/jenkins-template.pkr.hcl

@@ -119,9 +119,14 @@ EOF
 
   provisioner "shell" {
     inline = [
-      # Install Jenkins and its dependencies.
-      "curl -fsSL https://pkg.jenkins.io/debian/jenkins.io-2023.key | sudo tee /usr/share/keyrings/jenkins-keyring.asc > /dev/null",
-      "echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] https://pkg.jenkins.io/debian binary/ | sudo tee /etc/apt/sources.list.d/jenkins.list > /dev/null",
+      # Download Jenkins repository key and add it to the trusted keyrings.
+      "curl -fsSL https://pkg.jenkins.io/debian/jenkins.io-2023.key | sudo gpg --dearmor -o /usr/share/keyrings/jenkins-keyring.gpg",
+      "echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.gpg] https://pkg.jenkins.io/debian binary/ | sudo tee /etc/apt/sources.list.d/jenkins.list",
+
+      # Download the new Kubernetes community-owned repository key and add it to the trusted keyrings (to get apt-get update working).
+      "curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.28/deb/Release.key | sudo gpg --dearmor -o /usr/share/keyrings/kubernetes-apt-keyring.gpg",
+      "echo deb [signed-by=/usr/share/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.28/deb/ / | sudo tee /etc/apt/sources.list.d/kubernetes.list",
+
       # Sometimes apt-get uses IPv6 and causes failure, force to use IPv4 address.
       "sudo apt-get -qq -o Acquire::ForceIPv4=true update",
       "sudo apt-get -qq -o Acquire::ForceIPv4=true install -f -y ca-certificates openjdk-11-jre-headless",