[BUG][csharp][csharp-netcore] HttpClient is generated with an Obsolete warning.

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

The ApiClient is generated using an as Obsolete marked property that causes warnings in the generated project.

//'HttpRequestMessage.Properties' is obsolete: 'Use Options instead.'
if (options.Cookies != null && options.Cookies.Count > 0)
{
    request.Properties["CookieContainer"] = options.Cookies;
}

https://github.com/OpenAPITools/openapi-generator/blob/45336be84780480618d32b3609305cfacf0256e3/modules/openapi-generator/src/main/resources/csharp-netcore/libraries/httpclient/ApiClient.mustache#L389

https://github.com/dotnet/runtime/issues/34168

openapi-generator version

5.2.1 (technically Docker Image Tag: latest-release)

OpenAPI declaration file content or url

Haven't tried it, but should happen with PetShop.yaml.

Generation Details

csharp-netcore option "library" set to "httpclient".

Steps to reproduce

• Generate csharp-netcore client with httpclient setting.
• Compile generate code.
• Get warning.

Related issues/PRs

Suggest a fix

The change seem to be a year old, but I could not find a correct new implementation. ... so ... ¯\_(ツ)_/¯

Start with modules/openapi-generator/src/main/resources/csharp-netcore/libraries/httpclient/ApiClient.mustache at line 389 and review the generated HttpRequestMessage usage. Generate a csharp-netcore client with the httpclient library, compile it, and confirm the warning is removed while cookie handling still works.