port: New pipelines for the new vNextPrototype branch (#5912)

[github-actions[bot]]

The changes in New pipelines for the new vNextPrototype branch (#5912) may need to be ported to maintain parity with microsoft/botbuilder-dotnet.

Fixes #minor

Description

The new pipelines are vNext-BB-DotNet-CI-PR and vNext-BB-DotNet-CI-PR-(MacLinux).

In ADO they live here: https://dev.azure.com/FuseLabs/SDK_v4/_build?definitionScope=%5CDotNet%5CvNextPrototype

(There are a few tests failing in each.)

Changes:

yaml files added to new folder build\yaml\vnextprototype Comment fix in build/yaml/botbuilder-dotnet-ci.yml.

Please review and, if necessary, port the changes.