Tutorial websocket doc example

[ChihSeanHsu]

• Fix Tutorial websocket doc example #365 issue

As I mentioned in #365, change behavior of if statement in dependency function get_cookie_or_client.

Add fill session in cookie in get function to let session is assign ready.

[codecov]

Codecov Report

Merging #1540 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master     #1540    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          227       234     +7     
  Lines         6810      7004   +194     
==========================================
+ Hits          6810      7004   +194     

Impacted Files	Coverage Δ
.../test_tutorial/test_websockets/test_tutorial002.py	100.00% <100.00%> (ø)
tests/main.py	100.00% <0.00%> (ø)
fastapi/params.py	100.00% <0.00%> (ø)
fastapi/routing.py	100.00% <0.00%> (ø)
fastapi/encoders.py	100.00% <0.00%> (ø)
fastapi/applications.py	100.00% <0.00%> (ø)
fastapi/openapi/docs.py	100.00% <0.00%> (ø)
fastapi/openapi/utils.py	100.00% <0.00%> (ø)
tests/test_application.py	100.00% <0.00%> (ø)
fastapi/security/__init__.py	100.00% <0.00%> (ø)
... and 13 more

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[tiangolo]

Thanks! 🚀

I updated it a bit to use a query parameter instead of header as it would be easier to test during development. 🤓

Thanks for your contribution! 🍰 ☕