Add shipping rate price validation

[kswiatek92]

closes #5361

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 #5411 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #5411      +/-   ##
==========================================
- Coverage   91.13%   91.11%   -0.02%     
==========================================
  Files         283      283              
  Lines       18327    18333       +6     
  Branches     1607     1609       +2     
==========================================
+ Hits        16702    16704       +2     
- Misses       1196     1200       +4     
  Partials      429      429

Impacted Files	Coverage Δ
saleor/graphql/shipping/mutations.py	97.56% <100%> (+0.03%)	⬆️
saleor/core/utils/draftjs.py	20% <0%> (-10%)	⬇️
saleor/product/models.py	91.11% <0%> (-0.4%)	⬇️
saleor/demo/settings.py	0% <0%> (ø)	⬆️

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