[ES-12916] Add tags to PR-based benchmarks (#136185)

Author: gbanasiak

.buildkite/scripts/generate-pr-performance-benchmark.sh

@@ -46,6 +46,7 @@ steps:
         CONFIGURATION_NAME: ${GITHUB_PR_COMMENT_VAR_BENCHMARK}
         ENV_ID: ${env_id_baseline}
         REVISION: ${merge_base}
+        BENCHMARK_TYPE: baseline
   - label: Trigger contender benchmark with ${GITHUB_PR_TRIGGERED_SHA:0:7}
     trigger: elasticsearch-performance-esbench-pr
     build:
@@ -56,6 +57,7 @@ steps:
         ENV_ID: ${env_id_contender}
         ES_REPO_URL: https://github.com/${GITHUB_PR_OWNER}/${GITHUB_PR_REPO}.git
         REVISION: ${GITHUB_PR_TRIGGERED_SHA}
+        BENCHMARK_TYPE: contender
   - wait: ~
   - label: Update PR comment and Buildkite annotation
     command: |