Add an option second closure argument to the chunk Collection function

[troy-whitespark]

I propose that the ->chunk($int) function on collections be updated to ->chunk($int, $func = null) to match the chunk function on the Eloquent query builder. If the $func closure is passed, then the chunk function will pass it to ->each() on each of the chunks.

One common pattern I have when I'm writing a command that can process several hundred thousand database records is to allow an optional random-slice argument, it allows me to take a subset of the records so I can test that everything works before executing the big command. Because the command will process so many records, I generally like to chunk it.

Having this matching function signature will allow me to use either a query builder instance or a collection of actual items I pulled for testing purposes.

[mateusjunges]

Made a PR here #39065