Result of GetSensitivityLabels. Carries the (possibly empty) list of
Purview / SPE sensitivity labels attached to a single file. An empty array
means any of: feature flag off, vault not SPE-enabled, file has no
master-storage ref, unsupported extension, or Master Storage was
unreachable / returned unparseable JSON. The client must treat "empty" as
"show nothing" - this call is an advisory UX hint, never a security gate.
GetSensitivityLabelsResponse.label_info -- The labels of the file. An empty labels list means that no label information is available, not that the file is known to be unlabeled.