Add distributor per labelset received samples metric #10778

Job	Run time
build	4m 17s
test	16m 0s
lint	4m 24s
CodeQL	6m 49s
test-no-race	7m 16s
integration-configs-db	3m 7s
integration (requires_docker)	7m 28s
integration (integration_alertmanager)	4m 4s
integration (integration_backward_compatibility)	10m 55s
integration (integration_memberlist)	7m 32s
integration (integration_querier)	15m 39s
integration (integration_ruler)	5m 48s
integration (integration_query_fuzz)	4m 58s
deploy_website	0s
deploy	0s
	1h 38m 17s

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