Add parameter to New-UDAutocomplete -Multiple selection to only allow each option once

[pyramidofgreatness]

Summary of the new feature / enhancement

Currently when using New-UDAutocomplete -Multiple, the user can add the same item more than once.

It would be useful to have a parameter to disallow this behavior. For my use case, the majority of the time this would be the preferred functionality.

Proposed technical implementation details (optional)

Remove the selected item from the options list, or make it greyed out