Add trace headers to http subscriptions (#671) #1325

Job	Run time
setup	19s
validate-example (actor)	2m 16s
validate-example (configuration)	1m 25s
validate-example (conversation)	1m 31s
validate-example (crypto)	1m 12s
validate-example (dist-scheduler)	1m 1s
validate-example (grpc-service)	2m 17s
validate-example (hello-world)	54s
validate-example (pubsub)	1m 54s
validate-example (streamsub)	1m 7s
validate-example (service)	1m 55s
validate-example (socket)	45s
validate-example (workflow)	1m 30s
validate-example (workflow-parallel)	58s
	19m 4s

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