Menu-like components: add documentation showing custom onToggleKeydown implementation

[thatblindgeye]

Describe the enhancement or change
Followup to logic implemented in #11132. We should show a custom callback being used to reference for consumers - the custom menu with inline filter example would be a good choice.

Is this request originating from a Red Hat product team? If so, which ones and is there any sort of deadline for this enhancement?

Any other information?