Add support for manual checkpoints (#1709) #2051

Job	Run time
typecheck / typecheck	3m 34s
units / 🧪 Unit Tests	2m 12s
publish-webapp / publish	1m 42s
publish-worker / build (coordinator)	1m 38s
publish-worker / build (docker-provider)	51s
publish-worker / build (kubernetes-provider)	40s
	10m 37s

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