We just released Workflows v2, including the ability to use conditional logic to modify a quote when it's being built.

For this case, you can have a workflow triggered "When a quote is being built" and add a condition to "Only start when" the quote has both the Latte Art Printer and Iced Drinks.

Then, add an action of "Add add-on" and add your "Cold Foam" add-on.

Learn more about workflow conditions here: https://docs.flashquotes.com/workflows/conditions#condition-fields

Learn more about workflow actions here: https://docs.flashquotes.com/workflows/actions#quote-steps