Add cli option to output all strings in plain text in the Ignition config

[yasminvalim]

Created originally in Butane by @Zackaryia: coreos/butane#670

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Always output inlined or other source in plaintext if an option is passed to allow inspecting the .ign file more easily.

Reference #94 to see where the compression was added, and what files can be modified to undo it on feature flag.