dashboard/app: show manager unique coverage #15254

Job	Run time
build	12m 40s
arch (presubmit_arch_linux)	9m 5s
aux	3m 45s
dashboard	2m 31s
arch (presubmit_arch_freebsd)	5m 25s
race	14m 59s
arch (presubmit_arch_netbsd)	3m 17s
old	6m 5s
arch (presubmit_arch_openbsd)	3m 16s
gvisor	3m 14s
arch (presubmit_arch_darwin)	3m 33s
race_dashboard	3m 16s
arch (presubmit_arch_windows)	3m 7s
arch (presubmit_arch_executor)	2m 54s
	1h 17m 7s

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