Backport of #26427 to release/v7.6

Triggered by @adityapatwardhan on behalf of @TravisEz13

Original CL Label: CL-BuildPackaging

/cc @PowerShell/powershell-maintainers

Impact

REQUIRED: Choose either Tooling Impact or Customer Impact (or both). At least one checkbox must be selected.

Tooling Impact

• Required tooling change
• Optional tooling change (include reasoning)

This backports a fix for OneBranch pipeline condition syntax in the MSIX StoreBroker packaging pipeline. The original change ensures conditional expressions follow the correct OneBranch format, though the release branch already uses a more sophisticated dynamic channel selection approach.

Customer Impact

• Customer reported
• Found internally

Regression

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• Yes
• No

This is not a regression.

Testing

The fix addresses pipeline condition syntax to ensure proper OneBranch compatibility. The cherry-pick was successfully applied with conflict resolution that preserves the release branch's enhanced channel selection logic while incorporating the new instruction documentation.

Risk

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• High
• Medium
• Low

This is a build pipeline infrastructure change that adds documentation and was adapted to work with the existing sophisticated channel selection in the release branch. The changes only affect the MSIX packaging pipeline and preserve all existing functionality.

Merge Conflicts

Resolved conflict in .pipelines/templates/package-create-msix.yml where the main branch had split StoreBroker tasks into separate Preview/Stable tasks, but the release branch uses dynamic channel selection. Kept the release branch's more sophisticated approach while adding the new instruction documentation.