No way to provide transaction_tag with Partitioned DML update

[kberezin-nshl]

Is your feature request related to a problem? Please describe.
Not sure if that's a bug or a feature request. There is no way to assign a transaction_tag (not request tag!) to a partitioned DML transaction.

Describe the solution you'd like
Well, give us a way to optionally pass a transaction tag.

Additional context
We'd like to use transaction_tag-s to make improvements to our CDC mechanism which utilizes Change Streams. Unlike request tags, transaction tags make it all the way to change stream's data change records and we'd like to use that. Unfortunately, we can't do it when we do a massive updates using Partitioned DML.

[rahul2393]

@mayurkale22 Do you know if there are any plans to support tranasctionTags in partitionDML?
Currently we don't support it https://cloud.google.com/spanner/docs/introspection/troubleshooting-with-tags#mapping_between_api_methods_and_requesttransaction_tag

[rahul2393]

@dsimil there is no way for customers to captures updates from partitionDML in change streams, it only exports transaction_tag and for partitionDML sending transaction_tag is no-op