Add metric for number of series with discarded samples #13011

Job	Run time
test	11m 22s
lint	3m 20s
test-no-race	8m 52s
CodeQL	7m 12s
build	4m 55s
integration-configs-db	3m 6s
integration (integration_alertmanager)	4m 53s
integration (integration_memberlist)	8m 9s
integration (integration_ruler)	6m 7s
integration (integration_backward_compatibility)	12m 0s
integration (integration_query_fuzz)	5m 48s
integration (integration_querier)	16m 3s
integration (integration_remote_write_v2)	3m 10s
integration (requires_docker)	10m 58s
deploy_website	-1s
deploy	0s
	1h 45m 54s

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