Fix Searches

[dominik-zeglen]

I want to merge this change because it fixes (and refactors a bit) entity pickers with searchable fields.
Fixes #4471
Fixes #4472

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. The code is documented (docstrings, project documentation).
8. GraphQL schema and type definitions are up to date.
9. Changes are mentioned in the changelog.

[django-queries]

Here is the report for 725bd9d (mirumee/saleor @ fix/searches)
Base comparison is c098413.

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                     	         43	         43	             21

# 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               	          9	          9	              2

[codecov]

Codecov Report

Merging #4487 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4487      +/-   ##
==========================================
+ Coverage   90.71%   90.72%   +0.01%     
==========================================
  Files         291      291              
  Lines       16785    16785              
  Branches     1711     1711              
==========================================
+ Hits        15227    15229       +2     
+ Misses       1057     1056       -1     
+ Partials      501      500       -1

Impacted Files	Coverage Δ
saleor/payment/utils.py	91.34% <0%> (+0.86%)	⬆️

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