Improve error message when adding a PTransform with a name that already exists in the pipeline #19965
Description
Currently, when trying to apply a PTransform with a name that already exists in the pipeline, it returns a confusing error:
Transform "XXX" does not have a stable unique label. This will prevent updating of pipelines. To apply a transform with a specified label write pvalue | "label" >> transform
We'd like to improve this error message.
Imported from Jira BEAM-8415. Original Jira may contain additional context.
Reported by: davidyan.