Pubsub: add DirectRunner support for id_label and timestamp_attribute in Python SDK #18939
Description
At least for publishing (and maybe pulling) messages, non-Dataflow-based sources and sinks for Pub/Sub use the public API for Pub/Sub, which doesn't support id_label and timestamp_attribute settings.
Publishing:
id_label - add an attribute to each message with a unique value
timestamp_attribute - add an attribute to each message with the publishing time as its value
Pulling:
id_label - use the value of this message attribute to deduplicate messages
timestamp_attribute - use the value of this message attribute as the element's timestamp
Implementation details: could probably create a pubsubio.py module, for reuse with other runners (i.e. implement Pub/Sub IO as PTransforms and not NativeSinks and Sources).
Imported from Jira BEAM-4275. Original Jira may contain additional context.
Reported by: udim.