Replace File Polling With Pub Sub for GCS

[Goutam1511]

Currently, the Dataflow Deid Pipeline uses FileIo Watch transform to list existing files and poll for new files in the input GCS folder. This approach has a known Apache Beam issue that causes Out Of Memory(OOM) errors when the pipeline runs for a long time.The recommended solution is to use Pub/Sub notifications from GCS to detect new files instead of using polling. This will eliminate the OOM errors and improve the overall reliability of the pipeline.

Testing Conducted -

• Tested without --GCSNotificationTopic and --processExistingFiles=false flags
• Tested with only --GCSNotificationTopic flag
• Tested with default --processExistingFlags set to true
• Tested with both flags true
• Long running experiment started to capture throughput and memory improvements. Results will be captured internally.

[Goutam1511]

Added few comments @Goutam1511

@dup05 Addressed them. Kindly review and approve if all looks good.