Support `config` subcommand #62

Job	Run time
build (ubuntu-latest, latest)	31s
build (ubuntu-latest, nightly)	29s
build (macos-latest, latest)	38s
build (macos-latest, nightly)	37s
build (windows-latest, latest)	58s
build (windows-latest, nightly)	1m 11s
build (ubuntu-latest, 1.8.0)	27s
	4m 51s

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