Add ENABLE_DEBUG_TOOLBAR to settings

[koradon]

I want to merge this change because...
#3978

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.

[codecov]

Codecov Report

Merging #3983 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3983      +/-   ##
==========================================
+ Coverage   91.22%   91.28%   +0.06%     
==========================================
  Files         267      267              
  Lines       14443    14534      +91     
  Branches     1391     1387       -4     
==========================================
+ Hits        13176    13268      +92     
  Misses        897      897              
+ Partials      370      369       -1

Impacted Files	Coverage Δ
saleor/graphql/core/mutations.py	93.72% <0%> (-0.5%)	⬇️
saleor/graphql/product/bulk_mutations/products.py	100% <0%> (ø)	⬆️
saleor/graphql/shipping/bulk_mutations.py	100% <0%> (ø)	⬆️
saleor/graphql/menu/bulk_mutations.py	100% <0%> (ø)	⬆️
saleor/graphql/account/bulk_mutations.py	100% <0%> (ø)	⬆️
saleor/graphql/page/bulk_mutations.py	100% <0%> (ø)	⬆️
saleor/graphql/translations/mutations.py	100% <0%> (ø)	⬆️
...aleor/graphql/order/bulk_mutations/draft_orders.py	100% <0%> (ø)	⬆️
saleor/graphql/page/mutations.py	100% <0%> (ø)	⬆️
saleor/graphql/discount/bulk_mutations.py	100% <0%> (ø)	⬆️
... and 14 more

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[NyanKiyoshi]

Since it's a PR for the debug toolbar, could you take a minute to bump django-debug-toolbar-request-history to 0.0.10? I made a minor change to the toolbar's request history, it now shows the requests methods, which is quite useful for backend developers.

[NyanKiyoshi]

Should we really disable it by default?

[koradon]

If we don't want the next line
if DEBUG and ENABLE_DEBUG_TOOLBAR: then yes. Otherwise, it will be added on production servers by default and we for sure don't want that.

[koradon]

@NyanKiyoshi lets bump dependencies in another PR

[krzysztofwolski]

I strongly believe that DDT time has passed. Both storefront and dashboard use gql api + js front, and in this configuration DDT provides no feedback. Silk is in this area a much better choice.
Keeping that in mind I think that change default to have it disabled is a good choice.