Add cortex_ruler_rule_groups_in_store metric #8739

Job	Run time
build	4m 35s
test	21m 22s
lint	3m 55s
CodeQL	7m 32s
integration-configs-db	2m 10s
integration (requires_docker)	5m 50s
integration (integration_alertmanager)	4m 2s
integration (integration_backward_compatibility)	7m 28s
integration (integration_memberlist)	7m 28s
integration (integration_querier)	12m 23s
integration (integration_ruler)	4m 8s
integration (integration_query_fuzz)	2m 37s
deploy	0s
deploy_website	0s
	1h 23m 30s

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