Add validate for query param should be a valid string #4822

[nix010]

I want to merge this change because resolve #4822

Screenshots

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 ad69dfd (nix010/saleor @ feature/validate-query-param-string)
Base comparison is b92e705.

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                            	         15	         15	              3
  retrieve product attributes                	         13	         13	              2

# api.benchmark variant
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  retrieve variant list                      	         15	         15	              6

# api product sorting attributes
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  sort product not having attribute data     	         21	         21	              0

[codecov]

Codecov Report

Merging #4836 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4836      +/-   ##
==========================================
- Coverage   91.25%   91.25%   -0.01%     
==========================================
  Files         344      344              
  Lines       20623    20630       +7     
  Branches     1956     1958       +2     
==========================================
+ Hits        18819    18825       +6     
  Misses       1266     1266              
- Partials      538      539       +1

Impacted Files	Coverage Δ
saleor/graphql/views.py	82.84% <100%> (ø)	⬆️
saleor/graphql/webhook/mutations.py	91.83% <0%> (-0.56%)	⬇️
saleor/graphql/webhook/types.py	100% <0%> (ø)	⬆️

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[maarcingebala]

@nix010 could you also add entry about this change to the "Unreleased" section in the CHANGELOG.md file?

[nix010]

@maarcingebala yes. just added

[maarcingebala]

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