chore: manage kokoro graal image with renovate bot (#1736)

Author: mpeddada1

renovate.json

@@ -5,5 +5,16 @@
   "ignorePaths": ["*/**", "synthtool/gcp/templates/java_library/.kokoro/requirements.txt", "synthtool/docker/owlbot/java/src/requirements.txt"],
   "internalChecksFilter": "strict",
   "stabilityDays": 30,
-  "timezone": "America/Los_Angeles"
+  "timezone": "America/Los_Angeles",
+  "enabledManagers": ["regex"],
+  "regexManagers": [
+    {
+      "fileMatch": ["^synthtool/gcp/templates/java-library/.kokoro/presubmit/graalvm-native.*.cfg"],
+      "matchStrings": ["value: \"gcr.io/cloud-devrel-kokoro-resources/graalvm:(?<currentValue>.*?)\"",
+        "value: \"gcr.io/cloud-devrel-kokoro-resources/graalvm17:(?<currentValue>.*?)\""],
+      "depNameTemplate": "jdk",
+      "datasourceTemplate": "docker",
+      "packageNameTemplate": "ghcr.io/graalvm/jdk"
+    }
+  ]
 }