[BUG] [csharp-netcore] No way to pass proxy

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
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Description

Sorry I'm not shure if this a bug or feature request.

My client is generated with csharp-netcore.
I want to setup a proxy with the generated client. Here is mandatory not changig the generated code.

But there is actually no way to pass a proxy to the RestSharp client.
Everything is wrapped.

In Net framwork and Net core 3 its possible to setup a global proxy. But in Net core 2 its not possible.

Before using csharp-netcore i generated the client the client under targetframework net45.
Here i was able to use a proxy.

Example:

     var proxy = new WebProxy("http://localhost:3128")
      {
        Credentials = new NetworkCredential("USER", "PASS")
      };

      var config = new Configuration
      {
        BasePath = "https://my-example-api.com/api/v1",
        AccessToken = token.access_token
      };

      config.ApiClient.RestClient.Proxy = proxy;

In the same way its missed for netstandard.

openapi-generator version

4.1.3

OpenAPI declaration file content or url

Command line used for generation

java -jar "openapi-generator-cli-4.1.3.jar" generate -i api.yaml -g csharp-netcore -o Example.Client -p packageName=Example.Client

Steps to reproduce

Generate a csharp-netcore client and try to setup a proxy

Related issues/PRs

Suggest a fix

I think its needed to add api client configuration to the config in the same way like in Net framework

Start by generating the csharp-netcore client with the shown OpenAPI Generator 4.1.3 command, then inspect the generated Configuration and RestClient usage. Determine how proxy configuration differs for net45, netcoreapp3, and netstandard targets. Done means a generated client can receive and use a proxy without modifying generated code, with the relevant target frameworks still supported.