[Feature] OuiSplitButton - options - allow "disabled"

[pjfitzgibbons]

Is your feature request related to a problem? Please describe.
Recently released SplitButton has only "simple" options items - string or ReactNode.

I want to be able to have some option items displayed as "disabled" for cases where an item
should be presented to the user, though not available for selection at this time / in this context.

Describe the solution you'd like

Extend Options items to be string | ReactNode | SplitButtonOption where :

interface SplitButtonOption {
  disabled?: boolean;
  value?: string;
  display: string | ReactNode
}

Describe alternatives you've considered
OuiSuperSelect has "all the bells and whistles" for Options Items, though some of those features do not fit the context of SplitButton, like "inputDisplay" vs "dropdownDisplay". A simple extension of the existing type on SplitButton will do.

Additional context

Reference Issue #1187