Make multilevel cache backfilling async #8060

Job	Run time
test	17m 53s
lint	15m 39s
build	3m 48s
integration-configs-db	1m 54s
integration (requires_docker)	5m 15s
integration (integration_alertmanager)	4m 14s
integration (integration_backward_compatibility)	9m 56s
integration (integration_memberlist)	7m 29s
integration (integration_querier)	12m 35s
integration (integration_ruler)	3m 36s
integration (integration_query_fuzz)	1m 52s
deploy	0s
deploy_website	0s
	1h 24m 11s

Provide feedback