Add opt-in for default channel registrations check

[JaynieBai]

Add opt-in for default channel registrations check

Fixes #11214

Test with https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=11486318&view=logs&j=226748d0-f812-5437-d3f0-2dd291f5666e&t=b3ecf0d0-598d-5874-6547-0432d3f07f6b. but there is error

[Copilot]

Pull Request Overview

This pull request introduces an opt-in mechanism to enforce default channel registrations during the build. Key changes include:

• Adding a new boolean parameter "requireDefaultChannels" to the post-build template
• Forwarding the parameter through to the sdk-task invocation
• Enabling the parameter in the .vsts-dotnet pipeline configuration

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
eng/common/core-templates/post-build/post-build.yml	Adds a new boolean parameter and passes it to the build command
.vsts-dotnet.yml	Sets "requireDefaultChannels" to true to enforce the check in pipeline

Files not reviewed (1)

• eng/common/post-build/publish-using-darc.ps1: Language not supported