Organize nupkgs for publishing

[surajkrishnan14]

Description

This change:

• Modifies the post-build script to copy the unsigned nupkgs to the packages subdirectory under build\bin<arch>. This directory is monitored by internal pipelines to publish nuget packages.
• Updates the name of the core package to include the configuration in the generated name, for non-release configurations. eg. eBPF-for-Windows.Extensions.x64 for the "Release" configuration and eBPF-for-Windows.Extensions.Debug.x64 for the "Debug" configuration.

Testing

Internal pipelines were run and confirmed to publish the packages as expected