Add pull request check for validating changelogs (#100449)

Author: mark-vieira

.buildkite/pipelines/pull-request/validate-changelogs.yml

@@ -0,0 +1,9 @@
+steps:
+  - label: validate-changelogs
+    command: .ci/scripts/run-gradle.sh -Dignore.tests.seed validateChangelogs
+    timeout_in_minutes: 300
+    agents:
+      provider: gcp
+      image: family/elasticsearch-ubuntu-2004
+      machineType: custom-32-98304
+      buildDirectory: /dev/shm/bk