Upgrade GraphQL stack

[salwator]

Closes #1330

This PR also changes the behavior of resolve_products resolver. This function used to return products belonging to the given category and its descendants. This PR changes it not to include products from the descendant categories. This is consistent with the behavior of category index view in the storefront.

Pull Request Checklist

1. Privileged views and APIs are guarded by proper permission checks.
2. All visible strings are translated with proper context.
3. All data-formatting is locale-aware (dates, numbers, and so on).
4. Database queries are optimized and the number of queries is constant.
5. The changes are tested.
6. The code is documented (docstrings, project documentation).
7. Python code quality checks pass: pycodestyle, pydocstyle, pylint.
8. JavaScript code quality checks pass: eslint.

[codecov-io]

Codecov Report

Merging #1423 into master will decrease coverage by <.01%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master    #1423      +/-   ##
==========================================
- Coverage   82.44%   82.43%   -0.01%     
==========================================
  Files         131      131              
  Lines        5668     5665       -3     
  Branches      647      647              
==========================================
- Hits         4673     4670       -3     
  Misses        831      831              
  Partials      164      164

Impacted Files	Coverage Δ
saleor/product/utils.py	85.44% <ø> (-0.21%)	⬇️
saleor/graphql/utils.py	54.54% <100%> (ø)	⬆️
saleor/graphql/api.py	81.92% <93.93%> (ø)	⬆️

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[maarcingebala]

That distinct() was here to return proper results when there are multiple categories of the same name (this was added in PR #1331).