Make maxVatsOnline customizable to optimize resource usage #9574 (#10… #2684

Job	Run time
snapshot	1s
docker-parallel-build (linux/amd64)	7m 23s
docker-parallel-build (linux/arm64/v8)	1h 53m 18s
docker-sdk	11s
docker-solo	1m 7s
docker-ibc-alpha	29s
	2h 2m 29s

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