Proposal : option to use shtab for completion generation

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About this change: What it does, why it matters

Could be a draft for approval but was playing around with generating CLI docs from help strings and got a chance to play with shtab. Much lighter resource usage and does not execute underlying commands to generate completion. Added as an alternative option to argcomplete following the same method.

Not sure if this is better opened as a draft since it is technically a proposal