Add product price validation

[kswiatek92]

closes #5326

Pull Request Checklist

• Privileged queries and mutations are guarded by proper permission checks
• Database queries are optimized and the number of queries is constant
• Database migration files are up to date
• The changes are tested
• GraphQL schema and type definitions are up to date
• Changes are mentioned in the changelog

[codecov]

Codecov Report

Merging #5413 into master will decrease coverage by 0.01%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #5413      +/-   ##
==========================================
- Coverage   91.13%   91.11%   -0.02%     
==========================================
  Files         283      283              
  Lines       18329    18343      +14     
  Branches     1608     1613       +5     
==========================================
+ Hits        16704    16714      +10     
- Misses       1196     1200       +4     
  Partials      429      429

Impacted Files	Coverage Δ
saleor/graphql/product/mutations/products.py	95.84% <100%> (+0.03%)	⬆️
saleor/graphql/product/bulk_mutations/products.py	98.03% <50%> (+0.02%)	⬆️
saleor/core/utils/draftjs.py	20% <0%> (-10%)	⬇️
saleor/product/models.py	91.11% <0%> (-0.4%)	⬇️
saleor/graphql/shipping/mutations.py	97.53% <0%> (-0.04%)	⬇️
saleor/demo/settings.py	0% <0%> (ø)	⬆️

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[maarcingebala]

@kswiatek92 There are a few more places where we can set prices in API.

We have costPrice and priceOverride fields in:

• productVariantUpdate
• productVariantCreate
• productVariantBulkCreate

We should ensure that we have validation there as well. If it makes sense maybe we should add a function that does this validation and raises this error so don't have to duplicate entire ValidationError multiple times.

[kswiatek92]

@maarcingebala I don't think it's necessary,
there are only 3 places where this validation occurs, for different fields. To make it work properly, such function should have additional argument for field, and maybe message error, which make such function just ValidationError with different name

[fowczarek]

@kswiatek92
You can create function without restriction that you write.
As a function argument, you can pass price instead of mutation input. And function can return validation error with the message and you should catch this error in mutation body and add required ErrorCode.

@maarcingebala What do you think about introducing a specific error code for this validation?