dashboard/app: enable coverage pages formatting #16160

Job	Run time
dashboard	2m 42s
build	4m 18s
aux	4m 16s
race_dashboard	4m 1s
race	7m 18s
arch (presubmit_arch_freebsd)	6m 26s
arch (presubmit_arch_linux)	10m 32s
arch (presubmit_arch_netbsd)	3m 56s
arch (presubmit_arch_openbsd)	3m 55s
arch (presubmit_arch_darwin)	3m 50s
gvisor	3m 33s
arch (presubmit_arch_executor)	3m 22s
arch (presubmit_arch_windows)	3m 44s
old	6m 48s
	1h 8m 41s

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