Sylius-like upmerging strategy

[jakubtobiasz]

Description 📄

There's already a PR for upmerging between major branches, but I believe we should go with Sylius way, as it's already battle tested.

#240 (comment)

Small wins 🏆

• Changes between major branches are upmerged

Tips 💡

• https://github.com/Sylius/Sylius/blob/2.1/.github/workflows/upmerge_pr.yaml