Extend CI intake pipeline to run BC upgrade tests

.buildkite/scripts/get-bc-commit.sh

@@ -0,0 +1,59 @@
+#!/bin/bash
+
+#
+# Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+# or more contributor license agreements. Licensed under the "Elastic License
+# 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+# Public License v 1"; you may not use this file except in compliance with, at
+# your election, the "Elastic License 2.0", the "GNU Affero General Public
+# License v3.0 only", or the "Server Side Public License, v 1".
+#
+
+set -euo pipefail
+
+# Select the most recent build from the current branch.
+# We collect snapshots, order by date, then collect BCs, order by date, and concat them; then we select the last.
+# So if we have one (or more) BC, we will always prefer to use that. Otherwise we will use the latest snapshot.
+MANIFEST_URL="$(curl -s https://artifacts.elastic.co/releases/TfEVhiaBGqR64ie0g0r0uUwNAbEQMu1Z/future-releases/stack.json |
+jq ".releases[] |
+select(.branch == \"$BUILDKITE_BRANCH\") |
+select(.active_release == true) |
+((.snapshots | to_entries | sort_by(.value.completed_at)) +
+(.build_candidates | to_entries | sort_by(.value.completed_at))) |
+last | .value.manifest_url")"
+
+if [[ -z "$MANIFEST_URL" ]]; then
+   echo "No snapshots or build candidates for branch [$BUILDKITE_BRANCH]"
+   exit 0
+fi
+
+MANIFEST="$(eval "curl -s $MANIFEST_URL")"
+if [[ -z "$MANIFEST" ]]; then
+   echo "Cannot get the build manifest from [$MANIFEST_URL]"
+   exit 1
+fi
+
+TARGET_COMMIT_HASH=$(echo "$MANIFEST" | jq .projects.elasticsearch.commit_hash)
+TARGET_VERSION=$(echo "$MANIFEST" | jq .version)
+
+echo "Running bc-bwc tests on [$TARGET_VERSION] commit [$TARGET_COMMIT_HASH]"
+
+cat <<EOF | buildkite-agent pipeline upload
+steps:
+    - label: $BUILDKITE_BRANCH / bc-bwc
+      command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true -Dorg.elasticsearch.build.cache.push=true -Dignore.tests.seed -Dscan.capture-file-fingerprints -Dtests.bwc.main.version=${TARGET_VERSION} -Dtests.bwc.refspec.main=${TARGET_COMMIT_HASH} -Dtests.jvm.argline=\"-Des.serverless_transport=true\"
+      timeout_in_minutes: 300
+      agents:
+        provider: gcp
+        image: family/elasticsearch-ubuntu-2004
+        machineType: n1-standard-32
+        buildDirectory: /dev/shm/bk
+        preemptible: true
+      retry:
+        automatic:
+          - exit_status: \"-1\"
+            limit: 3
+            signal_reason: none
+          - signal_reason: agent_stop
+            limit: 3
+EOF