RATIS-2245. Ratis should wait for all apply transaction futures before taking snapshot and group remove #3765

Job	Run time
CI / build / build	1m 27s
CI / unit (server) / unit (server)	13m 6s
CI / unit (grpc) / unit (grpc)	11m 48s
CI / unit (misc) / unit (misc)	7m 3s
CI / basic (author) / author	7s
CI / basic (checkstyle) / checkstyle	31s
CI / basic (findbugs) / findbugs	1m 53s
CI / basic (rat) / rat	22s
CI / repro / repro	2m 49s
CI / compile (21) / compile (21)	1m 7s
CI / compile (17) / compile (17)	1m 7s
CI / compile (11) / compile (11)	1m 7s
CI / coverage	0s
	42m 27s

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