Add workflow for on-demand benchmarking #18

Job	Run time
set-models	13s
export-models (stories110M) / linux-job	12m 6s
build-llm-demo (tiktoken) / linux-job	33m 0s
build-llm-demo (bpe) / linux-job	32m 20s
upload-models	29s
upload-android-apps	1m 38s
	1h 19m 46s

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