[WIP] Add function to get prices for products from multiple supermarkets

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Please read through the checkjebon.js code.

Add a new function getPricesForProductsMultipleSupermarkets(productNames, supermarketCount, selectedSupermarkets), where selectedSupermarkets is an array of supermarkets that the user is willing to buy the products from, and supermarketCount the maximum number of supermarkets that the user wants to visit. For example, someone could want to visit a maximum of 3 supermarkets, and gives a list of 5 selected supermarkets.

This new method will assist people to visit multiple supermarkets and only buy the cheapest products at each supermarket. The outcome should be that the person can buy all the products from their shopping list from the cheapest stores. The output of the method therefor should list the supermarket(s) that combined are the cheapest, plus per supermarket the list of products that the user should buy there. \

Add an example in example.browser.html and example.node.js, where

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