Add error codes to API

[Kwaidan00]

I want to merge this change because it adds error codes for mutation errors.

It closes #4119.

Screenshots

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. GraphQL schema and type definitions are up to date.
8. Changes are mentioned in the changelog.

[maarcingebala]

I did the first review and I think we have to look through the codes and think whether we can unify/generalize some of them. Another question is whether we need to start exposing them all at once. Maybe a better idea would be to have dedicated enums for each group e.g. CheckoutErrorCodes.

[django-queries]

Here is the report for 702e735 (mirumee/saleor @ add-error-codes-in-api)
Base comparison is 9e68873.

No differences were found. (click me)

# api.benchmark checkout
  test name                           	left count 	right count	duplicate count
  ------------------------------------	-----------	-----------	---------------
  add billing address to checkout     	         34	         34	             20
  add shipping to checkout            	          7	          7	              0
  checkout payment charge             	         14	         14	              0
  complete checkout                   	          6	          6	              0
  create checkout                     	         48	         48	             24

# api.benchmark homepage
  test name                           	left count 	right count	duplicate count
  ------------------------------------	-----------	-----------	---------------
  retrieve main menu                  	          5	          5	              0
  retrieve product list               	          4	          4	              0
  retrieve secondary menu             	          5	          5	              0
  retrieve shop                       	          2	          2	              0

# api.benchmark product
  test name                           	left count 	right count	duplicate count
  ------------------------------------	-----------	-----------	---------------
  product details                     	         15	         15	              3

# api.benchmark variant
  test name                           	left count 	right count	duplicate count
  ------------------------------------	-----------	-----------	---------------
  retrieve variant list               	         18	         18	              8

[codecov]

Codecov Report

Merging #4676 into master will increase coverage by 0.07%.
The diff coverage is 89.76%.

@@            Coverage Diff             @@
##           master    #4676      +/-   ##
==========================================
+ Coverage   91.41%   91.49%   +0.07%     
==========================================
  Files         307      308       +1     
  Lines       18445    18572     +127     
  Branches     1844     1848       +4     
==========================================
+ Hits        16862    16992     +130     
+ Misses       1065     1063       -2     
+ Partials      518      517       -1

Impacted Files	Coverage Δ
saleor/graphql/order/utils.py	100% <100%> (ø)	⬆️
saleor/checkout/forms.py	94.47% <100%> (ø)	⬆️
saleor/graphql/shipping/mutations.py	98.21% <100%> (+0.01%)	⬆️
saleor/graphql/giftcard/mutations.py	98.64% <100%> (+0.01%)	⬆️
saleor/graphql/core/mutations.py	93.29% <100%> (+0.01%)	⬆️
saleor/account/validators.py	100% <100%> (ø)	⬆️
...aleor/graphql/order/bulk_mutations/draft_orders.py	100% <100%> (ø)	⬆️
saleor/graphql/account/utils.py	97.61% <100%> (+0.05%)	⬆️
saleor/checkout/utils.py	84.22% <100%> (+0.02%)	⬆️
saleor/graphql/account/mutations/staff.py	96.41% <100%> (+0.01%)	⬆️
... and 27 more

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #4676 into master will increase coverage by 0.28%.
The diff coverage is 96.36%.

@@            Coverage Diff             @@
##           master    #4676      +/-   ##
==========================================
+ Coverage   91.67%   91.96%   +0.28%     
==========================================
  Files         313      324      +11     
  Lines       18855    19491     +636     
  Branches     1851     1863      +12     
==========================================
+ Hits        17286    17925     +639     
+ Misses       1049     1047       -2     
+ Partials      520      519       -1

Impacted Files	Coverage Δ
saleor/core/weight.py	87.69% <ø> (ø)	⬆️
saleor/graphql/extensions/mutations.py	100% <100%> (ø)	⬆️
saleor/graphql/order/utils.py	100% <100%> (ø)	⬆️
saleor/checkout/forms.py	94.47% <100%> (ø)	⬆️
...aleor/graphql/account/mutations/service_account.py	97.53% <100%> (+0.38%)	⬆️
saleor/extensions/plugins/vatlayer/plugin.py	72.13% <100%> (+0.15%)	⬆️
saleor/graphql/menu/bulk_mutations.py	100% <100%> (ø)	⬆️
saleor/extensions/plugins/avatax/plugin.py	69.87% <100%> (+0.12%)	⬆️
saleor/graphql/giftcard/mutations.py	98.79% <100%> (+0.16%)	⬆️
saleor/account/error_codes.py	100% <100%> (ø)
... and 57 more

---

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[patrys]

Can we plan a meeting where we go through all of these codes and determine whether they are correct or even needed?

[Kwaidan00]

@patrys @maarcingebala I've created typed versions of Error type and separated enums. Please take a look.

[Kwaidan00]

@maarcingebala @korycins @NyanKiyoshi @patrys I've changed error code mechanism to use Meta class instead of inheritance, for some of your comments I've created separated issues, I've rebased branch and added error codes for new parts of the codebase.

[NyanKiyoshi]

❤️