[benchmark] Make H100 benchmark optional (#10908)

.buildkite/nightly-benchmarks/benchmark-pipeline.yaml

@@ -65,10 +65,15 @@ steps:
         - VLLM_USAGE_SOURCE
         - HF_TOKEN
 
+  - block: "Run H100 Benchmark"
+    key: block-h100
+    depends_on: ~
+
   - label: "H100"
     # skip: "use this flag to conditionally skip the benchmark step, useful for PR testing"
     agents:
       queue: H100
+    depends_on: block-h100
     plugins:
     - docker#v5.12.0:
         image: public.ecr.aws/q9t5s3a7/vllm-ci-postmerge-repo:$BUILDKITE_COMMIT