Enable package_metadata_sync_using_labels feature flag by default

Ahmad Zaydanrequested to merge
599534-enable-package-metadata-sync-using-labels into master

What does this MR do and why?

Toggles the package_metadata_sync_using_labels beta feature flag to default_enabled: true.

This enables the label-based fast path for package metadata sync for all instances, avoiding expensive listObjects calls when GCP bucket labels are available.

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