pkg/mgrconfig: export defaultValues function #18447

Job	Run time
gvisor	4m 0s
race_dashboard	2m 42s
old	7m 7s
build	4m 17s
aux	4m 55s
arch (presubmit_arch_darwin)	3m 41s
arch (presubmit_arch_windows)	3m 28s
race	6m 45s
arch (presubmit_arch_openbsd)	3m 44s
dashboard	1m 56s
arch (presubmit_arch_freebsd)	6m 19s
arch (presubmit_arch_executor)	3m 0s
arch (presubmit_arch_netbsd)	3m 42s
arch (presubmit_arch_linux)	10m 30s
	1h 6m 6s

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