Random number function for custom api

### Description

The title basically speaks for itself. I would love if a function returning random integer (in a range of integers) implemented for custom API widgets! Could be used e.g. for picking up random items from a json array

Start by locating the custom API widget implementation and how it processes JSON arrays. Define the random-integer function's range behavior and verify that it can be used to select random items from an array.

Written by the indexing model from the issue text.