Distinguish OrderLine product name and variant name

[fowczarek]

I want to merge this change because resolve #4624

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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 53b09ef (mirumee/saleor @ 4624/Distinguish_product_and_varinat_name_in_OrderLine)
Base comparison is e28546e.

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 #4702 into master will decrease coverage by 0.02%.
The diff coverage is 82.75%.

@@            Coverage Diff            @@
##           master   #4702      +/-   ##
=========================================
- Coverage   91.62%   91.6%   -0.03%     
=========================================
  Files         307     308       +1     
  Lines       18412   18438      +26     
  Branches     1825    1827       +2     
=========================================
+ Hits        16870   16890      +20     
- Misses       1036    1040       +4     
- Partials      506     508       +2

Impacted Files	Coverage Δ
saleor/core/analytics.py	85.29% <ø> (ø)	⬆️
saleor/product/models.py	93.31% <ø> (-0.7%)	⬇️
saleor/order/templatetags/order_lines.py	100% <100%> (ø)
saleor/order/models.py	90.15% <100%> (+0.07%)	⬆️
saleor/seo/schema/email.py	93.33% <33.33%> (-6.67%)	⬇️
saleor/graphql/order/types.py	90.9% <75%> (-0.48%)	⬇️
saleor/checkout/utils.py	84.02% <85.71%> (-0.04%)	⬇️
saleor/payment/utils.py	91.23% <0%> (+0.79%)	⬆️

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[korycins]

Is this comment obsolete?

[fowczarek]

I think yes. This comment explains why product_name have max_length=386. We can't change max length because we can't get new product_name for order lines with removed products or variants.

[korycins]

Shouldn't be str(line.variant) here?

[korycins]

And what about rest of calls of .display_product()? As @maarcingebala said, Do we need it at all? Maybe we can remove it.

[fowczarek]

1. No, because str(line.variant) is variant.name or variant.sku and display_product is product.name (variant.name). We need both names in analytics.
2. I think we shouldn't remove it because google merchant uses it.