Split store-gateway into index-gateway and chunks-gateway #64

Job	Run time
lint	3m 45s
build	5m 53s
test	33m 38s
integration-configs-db	3m 55s
integration (requires_docker)	11m 0s
integration (integration_alertmanager)	5m 19s
integration (integration_backward_compatibility)	18m 30s
integration (integration_memberlist)	6m 5s
integration (integration_querier)	26m 4s
integration (integration_ruler)	6m 51s
integration (integration_query_fuzz)	2m 59s
deploy	0s
deploy_website	0s
	2h 3m 59s

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