Drop webpack(er)

[damianlegawiec]

It can be easily added in via https://github.com/rails/webpacker#installation

However we encourage everyone to use Storefront API and SDK to build a custom Storefront UI

https://dev-docs.spreecommerce.org/getting-started/headless-commerce

Description

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• An overview of why the work is taking place (with any relevant links); don’t assume familiarity with the history.
• Major changes made and a high-level idea of the chosen approach.
• All the compromises made (in performance, readability, maintainability etc.)
  to achieve the expected result if any

Checklist

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• No unintended changes are included
• Spelling is correct
• There are tests covering new/changed functionality
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• Proper labels assigned. Use WIP label to indicate that state