add ring_members_by_zone metric if ring is zone aware #8209

Job	Run time
lint	16m 18s
build	4m 28s
test	17m 52s
integration-configs-db	1m 55s
integration (requires_docker)	5m 6s
integration (integration_alertmanager)	3m 49s
integration (integration_backward_compatibility)	7m 22s
integration (integration_memberlist)	7m 21s
integration (integration_querier)	12m 46s
integration (integration_ruler)	3m 43s
integration (integration_query_fuzz)	1m 45s
deploy_website	0s
deploy	0s
	1h 22m 25s

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