Fix: Update Pipeline for .NET 8 and modern Ubuntu runner

[nrs32]

This PR modernizes the Azure Pipeline configuration to use current versions of dependencies.

• Updates VM image from ubuntu-20.04 to ubuntu-latest
• Updates .NET SDK version from 6.x to 8.x to match project's target framework
• Adds explicit Node.js version pinning (20.x) via NodeTool@0
• Replaces deprecated node-sass with sass for compatibility with updated Node.js version
• Updates NuGetToolInstaller from version 0 to 1 with explicit version 6.x

Tested on my private Azure DevOps instance (after adding proj reference to models pkg); the pipeline succeeded.

[nrs32]

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