[ci] Refactor CI file structure (#29343)

.buildkite/test_areas/benchmarks.yaml

@@ -0,0 +1,19 @@
+group: Benchmarks
+depends_on: 
+  - image-build
+steps:
+- label: Benchmarks
+  timeout_in_minutes: 20
+  working_dir: "/vllm-workspace/.buildkite"
+  source_file_dependencies:
+  - benchmarks/
+  commands:
+  - bash scripts/run-benchmarks.sh
+
+- label: Benchmarks CLI Test
+  timeout_in_minutes: 20
+  source_file_dependencies:
+  - vllm/
+  - tests/benchmarks/
+  commands:
+  - pytest -v -s benchmarks/