[BUG] Installation Code from Generated README Missing Import Statements

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When working with the generated python client, Installation Code from Generated README are missing the Import Statements "Category" and "Tag" which does not allow that code to compile and run. Only after adding those import statements in, the code is runnable.

openapi-generator version

5.2.0-SNAPSHOT

OpenAPI declaration file content or url

https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/3_0/petstore.yaml

Generation Details

Using latest openapitools/openapi-generator-online:
Trying to generate a python client

Steps to reproduce

In Cgwin Terminal, run:

docker run -p 8888:8080 --entrypoint java openapitools/openapi-generator-online  -Dio.swagger.parser.util.RemoteUrl.trustAll=true -Dio.swagger.v3.parser.util.RemoteUrl.trustAll=true -jar /generator/openapi-generator-online.jar

In another Cgwin Terminal, run:

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' -d '{"openAPIUrl": "https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/3_0/petstore.yaml"}' 'http://localhost:8888/api/gen/clients/python'

Get Generated zip file from given URL

Follow Installation Instructions in Readme:

pip install git+https:////.git

Create installation.py in the python client based on README Installation Code:

import time
import openapi_client
from pprint import pprint
from openapi_client.api import pet_api
from openapi_client.model.api_response import ApiResponse
from openapi_client.model.pet import Pet
# Defining the host is optional and defaults to http://petstore.swagger.io/v2
# See configuration.py for a list of all supported configuration parameters.
configuration = openapi_client.Configuration(
    host = "http://petstore.swagger.io/v2"
)

# The client must configure the authentication and authorization parameters
# in accordance with the API server security policy.
# Examples for each auth method are provided below, use the example that
# satisfies your auth use case.

# Configure OAuth2 access token for authorization: petstore_auth
configuration = openapi_client.Configuration(
    host = "http://petstore.swagger.io/v2"
)
configuration.access_token = 'YOUR_ACCESS_TOKEN'


# Enter a context with an instance of the API client
with openapi_client.ApiClient(configuration) as api_client:
    # Create an instance of the API class
    api_instance = pet_api.PetApi(api_client)
    pet = Pet(
        id=1,
        category=Category(
            id=1,
            name="CbUUGjjNSwg0_bs9ZayIMrKdgNvb6gvxmPb9GcsM61ate1RA89q3w1l4eH4XxEz.5awLMdeXylwK0lMGUSM4jsrh4dstlnQUN5vVdMLPA",
        ),
        name="doggie",
        photo_urls=[
            "photo_urls_example",
        ],
        tags=[
            Tag(
                id=1,
                name="name_example",
            ),
        ],
        status="available",
    ) # Pet | Pet object that needs to be added to the store

    try:
        # Add a new pet to the store
        api_response = api_instance.add_pet(pet)
        pprint(api_response)
    except openapi_client.ApiException as e:
        print("Exception when calling PetApi->add_pet: %s\n" % e)

Compiler Complains about missing imports:

Only runs when These Two lines are Added:

from openapi_client.model.category import Category
from openapi_client.model.tag import Tag

Related issues/PRs

Suggest a fix

Reproduce the issue with the petstore.yaml specification and the Python client generation steps in the report. Inspect the generated README installation example and the generated Python models it uses; done means the example runs without manually adding the Category and Tag imports.