Filter empty labels from sharding key #8205

Job	Run time
lint	17m 36s
build	4m 0s
test	17m 54s
integration-configs-db	1m 56s
integration (requires_docker)	4m 58s
integration (integration_alertmanager)	3m 51s
integration (integration_backward_compatibility)	7m 19s
integration (integration_memberlist)	7m 1s
integration (integration_querier)	12m 29s
integration (integration_ruler)	3m 50s
integration (integration_query_fuzz)	2m 11s
deploy	0s
deploy_website	0s
	1h 23m 5s

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