Consider replacing uses of WebRequest with HttpClient

[glopesdev]

The WebRequest APIs have been marked as obsolete from .NET 6.0 onwards. They are currently used in only two places in the code base (in PackageViewController and DocumentationHelper). Some loose guidelines for replacing these deprecated APIs may be found in the references below:

• https://learn.microsoft.com/en-us/dotnet/api/system.net.http.httpclient?view=net-8.0
• https://stackoverflow.com/questions/70185058/how-to-replace-obsolete-webclient-with-httpclient-in-net-6