add `protocol` to aggregator api config/capabilities #4859

Job	Run time
janus_docker	40m 12s
janus_build (stable minus 2 releases)	31m 22s
janus_build (stable)	34m 52s
janus_interop_docker	29m 33s
janus_lints (stable minus 2 releases)	7m 53s
janus_lints (stable)	6m 14s
	2h 30m 6s

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