[BUG] [csharp-functions] custom packageName value is not used for usings in DefaultApi class

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

Generator used: csharp-functions
After generation and without 'human' changes, solution is not building.

1st issue:
After setting up custom packageName, DefaultApi file generated with it has wrong using.
It has default using Org.OpenAPITools.Models;, but should be using FirstName.RestApiServer.Models; in this case.

2nd issue is that it does not put using System.Collections.Generic;.

After manually fixing these 2 usings, solution is compiling with success.

openapi-generator version

Using latest docker image. First time using that generator, so do not know if it is regression.

OpenAPI declaration file content or url

openapi: '3.0.3'
info:
  title: TestApi
  description: xyz
  version: 1.0.0
servers:
  - url: 'https://xyz/api'
    description: Production server
  - url: 'localhost/api'
    description: TEST
paths:
  /test:
    get:
      summary: "Test if server is working"
      description: "Test if server is working"
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: string
  /matches:
    get:
      summary: "Get matches for user"
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  type: object
                  properties:
                    prop1:
                      type: integer
                    prop2:
                      type: string

Generation Details

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli generate `
    -i /local/spec.yml `
    -g csharp-functions `
    -o /local/out/server `
    --additional-properties=packageName=FirstName.RestApiServer

Steps to reproduce

1. Run generation command
2. Open solution in VS 2022.
3. Try to compile it

Results from VS:

Build started at 11:03...
1>------ Build started: Project: FirstName.RestApiServer, Configuration: Debug Any CPU ------
1>D:\repos\GeneratorBug\out\server\src\FirstName.RestApiServer\Functions\DefaultApi.cs(14,7,14,10): error CS0246: The type or namespace name 'Org' could not be found (are you missing a using directive or an assembly reference?)
1>D:\repos\GeneratorBug\out\server\src\FirstName.RestApiServer\Functions\DefaultApi.cs(21,40,21,72): error CS0246: The type or namespace name 'List<>' could not be found (are you missing a using directive or an assembly reference?)
1>D:\repos\GeneratorBug\out\server\src\FirstName.RestApiServer\Functions\DefaultApi.cs(21,45,21,71): error CS0246: The type or namespace name 'MatchesGet200ResponseInner' could not be found (are you missing a using directive or an assembly reference?)
1>Done building project "FirstName.RestApiServer.csproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
========== Build completed at 11:03 and took 01,268 seconds ==========

Related issues/PRs

Do not know

Suggest a fix

Something with using list.

Start by reproducing the issue with spec.yml, the csharp-functions generator, and packageName=FirstName.RestApiServer, then inspect the generated src/FirstName.RestApiServer/Functions/DefaultApi.cs. Compare its using directives with the reported compiler errors and rebuild the generated solution in Visual Studio. Done means the generated project builds without manually changing DefaultApi.cs.