Add .NET 6 Support

## Description
Add support for latest build in .NET 6 and update all .NET 5 builds to latest stable patch.

## Tasks
* Update all projects and sample code to compile with .NET 6
* Update all projects and sample code to compile with latest patch in .NET 5
* Update NuGet packages to ship .NET 5, .NET 6 and .NET 4.8
* Add build to compile and test with .NET48, .NET5, and .NET 6
