Fix dockerfiles for 3.0+

[tomaszszymanski129]

I want to merge this change because dockerfiles were not updated for a while and they should use the NEXT_PUBLIC_API_URI env var.

Screenshots

Pull Request Checklist

1. [ ] All visible strings are translated with proper context.
2. [ ] All data-formatting is locale-aware (dates, numbers, and so on).
3. [ ] The changes are tested.
4. [ ] The code is documented (docstrings, project documentation).
5. [ ] Changes are mentioned in the changelog.

Test Environment Config

API_URI=https://qa.staging.saleor.cloud/graphql/

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