Engine: Add the `await_processes` utility function #256

Job	Run time
amd64-build / build-test-upload	12m 28s
arm64-build / build-test-upload	12m 37s
amd64-push-ghcr / tag-push (aiida-core-base)	2m 15s
amd64-push-dockerhub / tag-push (aiida-core-base)	1m 50s
amd64-push-ghcr / tag-push (aiida-core-with-services)	2m 47s
amd64-push-dockerhub / tag-push (aiida-core-with-services)	2m 37s
arm64-push-ghcr / tag-push (aiida-core-base)	1m 37s
arm64-push-dockerhub / tag-push (aiida-core-base)	1m 25s
arm64-push-ghcr / tag-push (aiida-core-with-services)	1m 47s
arm64-push-dockerhub / tag-push (aiida-core-with-services)	2m 28s
merge-tags-dockerhub / merge-tags (aiida-core-base)	29s
merge-tags-dockerhub / merge-tags (aiida-core-with-services)	40s
merge-tags-ghcr / merge-tags (aiida-core-base)	37s
merge-tags-ghcr / merge-tags (aiida-core-with-services)	29s
	44m 6s

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