write python pseudocode for RabbitMQ queueing

[iannesbitt]

Current sysmwatch code demonstrates how to use the postgres NOTIFY service to listen for changes to tables in postgres. This task is to outline a design approach to:

1. reliably trigger a notify on relevant system metadata changes
2. subscribe to those notifications by listening via a python clinet connected to postgres
3. reliably enqueue a RabbitMQ message in the dataone-indexer queue for each event in Metacat that requires indexing

The current Java endopoints that handle this in Metacat are MetacatSolrIndex.submit() which calls IndexGenerator.publish(). We need to do a full scan of the code to see under what conditions the IndexGenerator.pubish(0 is being triggered and replicate that externally via the NOTIFY mechanism.

[mbjones]

@iannesbitt FYI, I found this article on using NOTIFY for message queues to be a very nice overview: https://worlds-slowest.dev/posts/postgresql-message-queue/. There is an associated python package (pg_mq) that shows a somewhat more complicated but more robust implementation of an exchange-based queue using NOTIFY/LISTEN.