dashboard/app: show manager unique coverage #14934

Job	Run time
aux	4m 48s
arch (presubmit_arch_linux)	10m 49s
build	11m 24s
arch (presubmit_arch_freebsd)	6m 23s
dashboard	3m 23s
arch (presubmit_arch_netbsd)	4m 25s
gvisor	4m 8s
arch (presubmit_arch_openbsd)	4m 23s
old	6m 45s
arch (presubmit_arch_darwin)	4m 21s
race	8m 48s
race_dashboard	4m 35s
arch (presubmit_arch_windows)	3m 29s
arch (presubmit_arch_executor)	3m 26s
	1h 21m 7s

Provide feedback