Add users stats http api to ingester #223

Job	Run time
CodeQL	6m 24s
lint	2m 29s
test	20m 46s
build	3m 51s
integration-configs-db	2m 11s
integration (requires_docker)	6m 24s
integration (integration_alertmanager)	4m 6s
integration (integration_backward_compatibility)	8m 49s
integration (integration_memberlist)	8m 19s
integration (integration_querier)	12m 14s
integration (integration_ruler)	4m 22s
integration (integration_query_fuzz)	2m 30s
deploy	0s
deploy_website	0s
	1h 22m 25s

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