Update the MSIXBundle-VPack pipeline to create VPack for both LTS and Stable channel packages

[daxian-dbw]

PR Summary

Update the MSIXBundle-VPack pipeline to create VPack for both LTS and Stable channel packages.

• Remove signed individual files from the output directory, to avoid the CredSign error that came from nowhere in the pipeline run on 4/23/26
• Update the pipeline to handle creating VPack packages for both the LTS and Stable channels
  • Create a matrix for the Pack stage with channel = lts and channel = stable
  • In each branch, decide whether skipping all steps based on LTSRelease.PublishToChannels defined in the metadata.json
  • Use different VPack package names for those 2 branches -- PowerShell7-LTS.Store.app and PowerShell7-Stable.Store.app