voption support

Since Perla has quite a lot of CLI configuration, I am looking through your implementation to see if there are any pain points when using FSharp.SystemCommandLine that I can improve upon.

Here are the possible API additions to FS.SCL that jumped out to me (all in the form of additions to the `Input` module) from within your "Commands.fs" file:
* `Input.optionMaybeV` (Kind of hard to find a great name for this due to the fact the S.CL overloaded the term "option").
* `Input.argumentMaybeV`
* `Input.arity`
* `Input.allowMultipleArgumentsPerToken`
* `Input.acceptOnlyFromAmong` (that takes a `string seq`)

Let me know if you can think of any others to add to the list.

Start in Commands.fs and review the Input module usage against the FSharp.SystemCommandLine API. Evaluate the proposed additions—optionMaybeV, argumentMaybeV, arity, allowMultipleArgumentsPerToken, and acceptOnlyFromAmong—and establish an agreed scope for which API improvements Perla needs.

Written by the indexing model from the issue text.