AWSS3Endpoints does not include GovCloud endpoints

[pksheldon4]

I've seen closed issue like this for minio-go dating back to 2017 but it does not work for dotnet. It should be as simple as adding these lines to AWSSEndpoints.cs

      // us-gov-east-1
      _ = endpoints.TryAdd("us-gov-east-1", "s3-us-gov-east-1.amazonaws.com");
      // us-gov-west-1
      _ = endpoints.TryAdd("us-gov-west-1", "s3-us-gov-west-1.amazonaws.com");

This prevents RequestUtil.MakeTargetURL(...) from setting the host to the default s3.amazonaws.com

I created a fork/branch but I don't understand the code base well enough to build/test it. A simple dotnet

[pksheldon4]

When I try to simply build the master branch of this project I get numerous code-analysis errors which make building/testing impossible