RATIS-2248. Rename CI workflows to .yaml #1

Job	Run time
CI / build / build	1m 20s
CI / basic (author) / author	10s
CI / basic (rat) / rat	20s
CI / basic (checkstyle) / checkstyle	23s
CI / unit (grpc) / unit (grpc)	11m 18s
CI / unit (misc) / unit (misc)	7m 19s
CI / basic (findbugs) / findbugs	1m 42s
CI / unit (server) / unit (server)	12m 51s
CI / repro / repro	1m 12s
CI / compile (11) / compile (11)	1m 3s
CI / compile (17) / compile (17)	1m 0s
CI / compile (21) / compile (21)	1m 1s
CI / coverage	0s
	39m 39s

Provide feedback