Add query endpoint for subcribers who are validators, simplify AddPublisher proposal #904

Job	Run time
sommelier-build	18m 15s
hardhat-build	1m 54s
integration-tests (ScheduledCork)	4m 24s
integration-tests (AxelarCork)	5m 53s
integration-tests (Auction)	2m 39s
integration-tests (CellarFees)	4m 0s
integration-tests (Incentives)	7m 8s
integration-tests (Pubsub)	5m 14s
	49m 27s

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