chore: add kokoro job for verifying presence of docker image

.kokoro/presubmit/graalvm-docker.cfg

@@ -0,0 +1,12 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+  key: "TRAMPOLINE_IMAGE"
+  value: "gcr.io/cloud-devrel-kokoro-resources/java8"
+}
+
+env_vars: {
+  key: "TRAMPOLINE_BUILD_FILE"
+  value: "github/java-shared-config/.kokoro/verify-docker-images.sh"
+}

.kokoro/verify-docker-images.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+# Script to verify the presence of GraalVM docker test images tagged with the latest java-shared-config version.
+
+function fetch_image_names() {
+  imageNames="$(grep "  - gcr.io/cloud-devrel-public-resources/" .cloudbuild/cloudbuild.yaml | cut -d "/" -f 3 | cut -d ":" -f 1)"
+  export imageNames
+  echo "$imageNames"
+}
+
+# Get the directory of the build script
+scriptDir=$(realpath "$(dirname "${BASH_SOURCE[0]}")")
+# cd to the parent directory, i.e. the root of the git repo
+cd ${scriptDir}/.. || exit
+
+# Fetch the java-shared-config version in source of the current commit.
+javaSharedConfigVersion="$(mvn help:evaluate -Dexpression=project.version -q -DforceStdout)"
+
+branchName=$(git name-rev "$KOKORO_GIT_COMMIT" | sed 's/.* //')
+gitCommitMessage=$(git log -1 "$(git rev-parse --short "$KOKORO_GIT_COMMIT")" | grep "chore(main): release *")
+
+# GraalVM docker images are not tagged with SNAPSHOT versions.
+if [[ "${branchName}" == *"release-please--branches--main"* ]] && [[ ! $gitCommitMessage =~ "SNAPSHOT" ]]; then
+  imageNames=$(fetch_image_names)
+  for name in $imageNames; do
+    fullContainerName="gcr.io/cloud-devrel-public-resources/${name}:${javaSharedConfigVersion}"
+    echo "Verifying presence of ${fullContainerName}."
+    gcloud container images describe "${fullContainerName}" > /dev/null; exit_status=$?
+    if [[ $exit_status = 0 ]]; then
+      echo "Success. Found $fullContainerName."
+    fi
+  done
+  RETURN_CODE=$?
+else
+  echo "Skipping check for non-release and SNAPSHOT update branches"
+  exit 0
+fi