Add .NET Core SDK 8.x to Pipeline for release8.x branch

[WanjohiSammy]

This pull request adds a new task to the pipeline to use the .NET Core SDK version 8.x. The task configuration includes the following:

  - task: UseDotNet@2
      displayName: Use .NET Core sdk 8.x
      inputs:
        version: 8.x
        includePreviewVersions: true

This update ensures that the pipeline can support .NET Core 8.x changes.