Check whether picocli can be customized to automatically convert `_` to `-` in enum values

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For consistency, enum values passed on the command line should use - as word separator, however enum values cannot contain a - character. We have various Converter and Iterable implementations to convert - to _ and vice versa, for example:

• OutputFormatConfigConverter (also covers some additional functionality)
• ProgressWriterTypeConverter

We should check whether there's any way to have picocli automatically handle the _ to/from - conversion when processing option values and generating completion candidates.

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See https://github.com/remkop/picocli/issues/2025

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We've now identified a much easier way to handle this; enum's can simply provide a toString() method like the following:

        @Override
        public String toString() {
            // Show and accept dashes instead of underscores when this
            // enum is used in picocli options.
            return name().replace('_', '-');
        }

Picocli will display the toString() value as completion candidates, and also properly resolve enum values when specified with dashes on the command line.