Migrate to django-prices 2.1

[NyanKiyoshi]

Closes #4337, fixes #4636, fixes #4378.

TBD

• Rebase
• Added missing relation fields and verbose_name mirumee/django-prices#90;
• Release of django-prices 2.1

Dashboard 1.0

• Update product form
• Update product variant form

GraphQL

• Fix accidental refactor of inputs
• Deprecate invalid naming in the graphql types

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.

[django-queries]

Here is the report for d28c53c (NyanKiyoshi/saleor @ django-prices/migrate/2.0)
Base comparison is 1ac9086.

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                     	         13	         13	              3

# api.benchmark variant
  test name                           	left count 	right count	duplicate count
  ------------------------------------	-----------	-----------	---------------
  retrieve variant list               	         15	         15	              8

[codecov]

Codecov Report

Merging #4639 into master will decrease coverage by 0.04%.
The diff coverage is 91.51%.

@@            Coverage Diff             @@
##           master    #4639      +/-   ##
==========================================
- Coverage   91.37%   91.33%   -0.05%     
==========================================
  Files         308      308              
  Lines       18235    18339     +104     
  Branches     1814     1830      +16     
==========================================
+ Hits        16663    16750      +87     
- Misses       1058     1068      +10     
- Partials      514      521       +7

Impacted Files	Coverage Δ
saleor/graphql/product/types/products.py	91.88% <ø> (ø)	⬆️
saleor/dashboard/product/filters.py	100% <ø> (ø)	⬆️
saleor/extensions/plugins/vatlayer/plugin.py	71.59% <ø> (ø)	⬆️
saleor/dashboard/order/filters.py	91.17% <ø> (ø)	⬆️
saleor/graphql/order/mutations/orders.py	95.02% <ø> (ø)	⬆️
saleor/extensions/plugins/avatax/__init__.py	77.88% <0%> (ø)	⬆️
saleor/dashboard/order/utils.py	76.47% <0%> (ø)	⬆️
saleor/extensions/plugins/avatax/plugin.py	67.72% <100%> (ø)	⬆️
saleor/dashboard/widgets.py	91.3% <100%> (-0.37%)	⬇️
saleor/graphql/giftcard/mutations.py	98.63% <100%> (ø)	⬆️
... and 33 more

---

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

Codecov Report

Merging #4639 into master will increase coverage by <.01%.
The diff coverage is 95.18%.

@@            Coverage Diff             @@
##           master    #4639      +/-   ##
==========================================
+ Coverage   91.41%   91.41%   +<.01%     
==========================================
  Files         307      307              
  Lines       18445    18542      +97     
  Branches     1844     1856      +12     
==========================================
+ Hits        16862    16951      +89     
- Misses       1065     1070       +5     
- Partials      518      521       +3

Impacted Files	Coverage Δ
saleor/graphql/product/types/products.py	91.9% <ø> (ø)	⬆️
saleor/dashboard/product/filters.py	100% <ø> (ø)	⬆️
saleor/extensions/plugins/vatlayer/plugin.py	71.59% <ø> (ø)	⬆️
saleor/dashboard/order/filters.py	91.17% <ø> (ø)	⬆️
saleor/graphql/order/mutations/orders.py	95.02% <ø> (ø)	⬆️
saleor/extensions/plugins/avatax/__init__.py	77.88% <0%> (ø)	⬆️
saleor/extensions/plugins/avatax/plugin.py	67.72% <100%> (ø)	⬆️
saleor/graphql/giftcard/mutations.py	98.63% <100%> (ø)	⬆️
saleor/product/utils/variants_picker.py	94.91% <100%> (ø)	⬆️
saleor/shipping/models.py	80% <100%> (+0.66%)	⬆️
... and 38 more

---

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[NyanKiyoshi]

A lot of the money logic really needs refactoring as it was never meant to be able to handle multiple currencies. Overall, it should be able to handle having different currencies, e.g. the storefront owner changed the default currency. But it is not meant to be achievable.

For now we only want to upgrade to the latest django-prices to fix a blocking bug (#4378) and once we get the time for it, we will implement proper multi-currency support, which shouldn't have any dependency on the settings' default currency.

[Kwaidan00]

@NyanKiyoshi you're right, a lot of code will have to be refactored for multi-currency support. I think the hardest part will be sorting and filtering stuff. And of course checking if values in sum has the same currency - or catching exception.