Add payment authorize and charge mutation

[jxltom]

This PR adds payment's authorize and charge mutation, as well as the tests. Ready for view.

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. Database migration files are up to date.
6. The changes are tested.
7. The code is documented (docstrings, project documentation).
8. GraphQL schema and type definitions are up to date.

[codecov]

Codecov Report

Merging #3426 into master will increase coverage by 0.04%.
The diff coverage is 90.69%.

@@            Coverage Diff            @@
##           master   #3426      +/-   ##
=========================================
+ Coverage   89.66%   89.7%   +0.04%     
=========================================
  Files         237     237              
  Lines       12860   12901      +41     
  Branches     1299    1301       +2     
=========================================
+ Hits        11531   11573      +42     
  Misses        922     922              
+ Partials      407     406       -1

Impacted Files	Coverage Δ
saleor/graphql/payment/schema.py	100% <100%> (ø)	⬆️
saleor/graphql/payment/mutations.py	87.83% <90%> (+0.68%)	⬆️
saleor/payment/utils.py	97.72% <0%> (+2.27%)	⬆️
saleor/payment/gateways/dummy/__init__.py	100% <0%> (+4.08%)	⬆️

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