[Housekeeping] [flytekit] Move input parsing to importable package

[wild-endeavor]

Task

Small cleanup task. The literal converter that works with click parsing would be useful to have separately. Move this out to a different folder so we can use it in other parts of the codebase.

Related to #208

Misc

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[cosmicBboy]

Move the literal converter out of the click modules and expose this as a flytekit module