dashboard/app: show manager unique coverage #15192

Job	Run time
aux	4m 8s
arch (presubmit_arch_linux)	3m 57s
dashboard	2m 56s
arch (presubmit_arch_freebsd)	4m 2s
build	1m 55s
gvisor	3m 29s
arch (presubmit_arch_netbsd)	4m 1s
arch (presubmit_arch_openbsd)	4m 2s
old	6m 52s
race	7m 47s
arch (presubmit_arch_darwin)	4m 2s
race_dashboard	4m 26s
arch (presubmit_arch_windows)	3m 24s
arch (presubmit_arch_executor)	3m 23s
	58m 24s

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