Add the --ext parameter to the split command

[romanpryshliak]

Is your feature request related to a problem? Please describe.

Please add the --ext parameter to the split command and convert JSON to YAML and vice versa.

The bundle command has that parameter, so if you get a file in JSON format and you want YAML, you have to split it, bundle it with --ext to convert it, then split it again.

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[lornajane]

Thanks for passing on this suggestion! One immediate comment I have is that it sounds like the first split operation could be omitted without any change in output - run bundle to get the target output format, and then run split to get the output in the desired structure.