Replace labels assigned to a resource target

Replaces the complete label set for one target atomically, ignoring label IDs that do not exist in the caller's organization and removing stale assignments. The response contains only existing label IDs. Concurrent replacements use last-write-wins semantics. The operation requires only the target resource's update permission: dashboards|update, datasets|update, monitors|update, or notifiers|update. Datasets must also be readable, writable, and owned by the caller's organization. Monitor dataset permissions match those required to read the monitor. A target that uses the wrong identifier for its type returns 400. An unknown target type, duplicate label IDs, and more than 500 label IDs fail request validation with 422. A target that does not exist or is not owned by the caller's organization returns 404.