FC-0001: ecommerce Basket Page -> micro-frontend (make the column nullable)

[UvgenGen]

Description

This is a first part of removing ecommerce's older implementation of the Django-server-side rendering of the Basket Page.
Second part: #3718

Updated the model and generate a migration making the column nullable (null=True)

Supporting information

openedx/public-engineering#68
Original Jira Issue: https://openedx.atlassian.net/browse/DEPR-42
PR to edx-platform: openedx/edx-platform#30377
Second part: #3718

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