[Python] API Key sharing between Configuration instances (port the 2.x fix)

Description

Swagger-codegen version

3.0.22

In 3.0.x the instances of the Configuration Python class generated still share the api_key. This has been fixed in 2.4: https://github.com/swagger-api/swagger-codegen/issues/9117

Steps to reproduce

I confirmed that, after creating 2 instances of Configuration changing the content of the api_key dict on one instance changes its content in the other:

>>> from my_client import Configuration
>>> c1 = Configuration()
>>> c1.api_key['Authorization'] = "c1 auth"
>>> c2 = Configuration()
>>> c2.api_key['Authorization'] = "c2 auth"
>>> for c in [c1, c2]:
...     print(c.api_key)
...
{'Authorization': 'c2 auth'}
{'Authorization': 'c2 auth'}

Related issues/PRs

https://github.com/swagger-api/swagger-codegen/issues/9117

Suggest a fix/enhancement

The fix for https://github.com/swagger-api/swagger-codegen/issues/9117 (https://github.com/swagger-api/swagger-codegen/pull/9130) could conceivably be ported to 3.0.0.

Start with the generated Python Configuration class and compare its api_key handling with the 2.4 fix in issue #9117 and pull request #9130. Reproduce the two-instance example from this issue; done means changing one instance's api_key no longer changes the other.