[core][kuberay] Trigger kuberay release pipeline from rayci (#51539)

tighter integration test with kuberay

---------

Signed-off-by: dayshah <dhyey2019@gmail.com>

Author: dayshah

.buildkite/release-automation/pre_release.rayci.yml

@@ -51,6 +51,19 @@ steps:
         RAYCI_RELEASE: 1
         RAYCI_SCHEDULE: "nightly"
 
+  - label: "Trigger :kubernetes: Kuberay CI Tests"
+    if: build.env("RAYCI_WEEKLY_RELEASE_NIGHTLY") == "1"
+    trigger: "ray-ecosystem-ci-kuberay-ci"
+    key: trigger-kuberay
+    depends_on: trigger-postmerge-nightly
+    build:
+      branch: "release-1.3"
+      message: "Triggered by release-automation build #${BUILDKITE_BUILD_NUMBER}"
+      env:
+        # KubeRay CI will pull an image based on this commit and the current date
+        RAY_NIGHTLY_COMMIT: "${BUILDKITE_COMMIT}"
+        IS_FROM_RAY_RELEASE_AUTOMATION: 1
+
   - label: "Trigger Postmerge MacOS test"
     key: trigger-postmerge-macos
     trigger: "postmerge-macos"