Add user id to jwt payload

[salwator]

This PR extends JWT payload with additional user global ID to make it easier to use the saleor with other services in a federation, token now contains graphql type key so nothing more is needed to get user data from saleor in a query.
Additionally, it adds email as key to User graphql type as it may be a more convenient identifier.

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.

[codecov]

Codecov Report

Merging #5039 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #5039      +/-   ##
==========================================
+ Coverage   90.89%   90.89%   +<.01%     
==========================================
  Files         294      294              
  Lines       18269    18273       +4     
  Branches     1679     1680       +1     
==========================================
+ Hits        16605    16610       +5     
+ Misses       1228     1227       -1     
  Partials      436      436

Impacted Files	Coverage Δ
saleor/graphql/utils.py	91.57% <100%> (+0.08%)	⬆️
saleor/graphql/account/types.py	96.1% <100%> (+0.48%)	⬆️

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[django-queries]

Here is the report for 451ebc0 (mirumee/saleor @ add-user-id-to-jwt-payload)
Base comparison is 81383c0.

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                    	         10	         10	              0
  complete checkout                          	          8	          8	              0
  create checkout                            	         50	         50	             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                	          9	          9	              0

# api.benchmark variant
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  product variant bulk create                	         51	         51	              3
  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