Update target frameworks to netstandard2.0;netstandard2.1;net8.0;net10.0

[gavinbarron]

Summary

Update the SDK target frameworks from netstandard2.0;netstandard2.1;net5.0 to netstandard2.0;netstandard2.1;net8.0;net10.0.

This is a breaking change as we are dropping support for net5.0 (which is EOL) and adding net8.0 and net10.0.

Changes needed

• Update TFMs in Microsoft.Graph.Beta.csproj
• Update test project to target net8.0 and net10.0
• Update CI/CD pipelines to install .NET 10 SDK
• Simplify per-TFM build steps in pipelines