Update: Linux pipeline to use custom pool

[Tatsinnit]

Description

This PR take care of the pool which is no longer valid and with the new custom pool there is a need to use the dot net task so that the esrpcli.exe: not found error can be avoided.

This is preemptive change and helps in updating the pipeline. There is more required for moving forward, like:

• Moving the 1es out to the ../workflow/.azure/.pipeline or whatever preferred space folks want to.
• Secondly, there is a need to co-rdinate the move-around changes in the 1es pipeline as well.

Thanks

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring
• CI/CD changes
• Other: **___**

Changes Made

• List the specific changes made are as follows:
  • Poolname change.
  • Consecutive botnet task required because there will be esop not found error with custom image.

[Copilot]

Pull request overview

This PR updates the Linux 1ES pipeline to use a new custom pool image and adds .NET SDK installation to fix ESRP Code Signing compatibility issues. The previous pool image is no longer valid, and the new custom image requires .NET SDK to be explicitly installed to avoid "esrpcli.exe: not found" errors.

Changes:

• Updated pool image from azcu-1es-agent-amd64-mariner-2-img to 1es-azlinux-3-amd64-custom-disk
• Added UseDotNet@2 task to install .NET SDK 6.x for ESRP signing compatibility

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[ashu8912]

Saw the same change done in the k8s extension as well so i know this works, thanks @Tatsinnit

[illume]

I wonder how do we verify this workflow is working? Can we run it to generate executables? Or is it tied to a release?
@Tatsinnit I remember now you posted docs already on how to do the builds, I'll read through those.