Add workflow for on-demand benchmarking #3306

Job	Run time
gather-models	8s
test-arm-backend-delegation / linux-job	15m 19s
test-arm-reference-delegation / linux-job	15m 2s
test-coreml-delegate / macos-job	45m 57s
test-custom-ops-macos (cmake) / macos-job	11m 46s
test-demo-backend-delegation (buck2) / linux-job	5m 53s
test-demo-backend-delegation (cmake) / linux-job	5m 7s
test-llama-runner-mac (fp32, buck2, coreml) / macos-job	1m 21s
test-llama-runner-mac (fp32, buck2, mps) / macos-job	1m 24s
test-llama-runner-mac (fp32, buck2, portable) / macos-job	9m 52s
test-llama-runner-mac (fp32, buck2, xnnpack+kv+custom) / macos-job	9m 43s
test-llama-runner-mac (fp32, cmake, coreml) / macos-job	11m 8s
test-llama-runner-mac (fp32, cmake, mps) / macos-job	12m 21s
test-llama-runner-mac (fp32, cmake, portable) / macos-job	12m 13s
test-llama-runner-mac (fp32, cmake, xnnpack+kv+custom) / macos-job	11m 17s
test-selective-build-macos (cmake) / macos-job	10m 20s
test-pybind-build-macos (cmake) / macos-job	8m 37s
test-models-macos (cmake, mv3, portable, macos-m1-stable, 90) / macos-job	7m 49s
test-models-macos (cmake, mv3, xnnpack-quantization-delegation, macos-m1-stable, 90) / macos-job	13m 41s
test-models-macos (cmake, vit, portable, macos-m1-stable, 90) / macos-job	8m 23s
test-models-macos (cmake, vit, xnnpack-delegation, macos-m1-stable, 90) / macos-job	12m 46s
	3h 50m 7s

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