🐛 Fix support for extending openapi_extras with parameter lists

[orilevari]

Issue

When specifying parameters in openapi_extras for an endpoint, they will overwrite the existing query parameters with the extra parameters. This is due to deep_dict_update in utils.py overwriting list types rather than merging them together.

PR Content

This PR updates deep_dict_update to merge arrays instead of overwriting. I have also added a test case that demonstrates and verifies the desired behavior.

Testing

Ran bash scripts/test-cov-html.sh with 100% test pass including new test case

[tiangolo]

Awesome, thanks for the contribution @orilevari! 🚀 🎉

[codecov]

Codecov Report

Merging #4267 (7c8e75a) into master (92181ef) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #4267   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          534       535    +1     
  Lines        13811     13830   +19     
=========================================
+ Hits         13811     13830   +19     

Impacted Files	Coverage Δ
fastapi/utils.py	100.00% <100.00%> (ø)
tests/test_openapi_query_parameter_extension.py	100.00% <100.00%> (ø)

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[Darep]

Is there a way to fall back to the old functionality somehow? 🤔 We have Query(default=datetime.utcnow()) and we are trying to override it like openapi_extra={"parameters": [{"schema": {"default": "Current timestamp in UTC"}}]} 😄 And this change now simply appends a new parameter in the list.

We might do include_in_schema=False and write it completely if there isn't, so no worries... 😊 (Other solutions for changing the default in the OpenAPI-schema also welcome!)