RATIS-2248. Rename CI workflows to .yaml (#1220) #2

Job	Run time
CI / build / build	1m 19s
CI / basic (findbugs) / findbugs	1m 55s
CI / basic (checkstyle) / checkstyle	21s
CI / basic (author) / author	8s
CI / basic (rat) / rat	23s
CI / unit (grpc) / unit (grpc)	12m 0s
CI / unit (misc) / unit (misc)	7m 18s
CI / unit (server) / unit (server)	13m 14s
CI / repro / repro	1m 10s
CI / compile (17) / compile (17)	1m 4s
CI / compile (21) / compile (21)	1m 6s
CI / compile (11) / compile (11)	56s
CI / coverage	2m 37s
	43m 31s

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