[python-experimental] Quicken package loading (#6437)

* apis and models contains all apis and models, omits loading them in the package namespace

* Runs git add -a and commits it

* Fixes test_outer_enum.py

* Fixes test_fruit.py

* Updates test_fruit and test_mammal

* Fixes test_parent_pet

* Updates test_discard_unknown_properties.py

* Updates test_deserialization.py

* Updates v2 docs md files for apis + the readme

* Fixes v2 tests

* v2 doc updates

* Updates v3 docs

* Reverts python_doc_auth_partial.mustache

* Adds sys to v3 tests

* Adds FILES update

Co-authored-by: Justin Black <justinblack@justins-air.lan>

samples/openapi3/client/petstore/python-experimental/docs/DefaultApi.md

@@ -18,6 +18,8 @@ Method | HTTP request | Description
 from __future__ import print_function
 import time
 import petstore_api
+from petstore_api.api import default_api
+from petstore_api.model import inline_response_default
 from pprint import pprint
 # Defining the host is optional and defaults to http://petstore.swagger.io:80/v2
 # See configuration.py for a list of all supported configuration parameters.
@@ -29,7 +31,7 @@ configuration = petstore_api.Configuration(
 # Enter a context with an instance of the API client
 with petstore_api.ApiClient() as api_client:
     # Create an instance of the API class
-    api_instance = petstore_api.DefaultApi(api_client)
+    api_instance = default_api.DefaultApi(api_client)
     
     # example, this endpoint has no required or optional parameters
     try: