R1:ba833805656e

Update the "Notification Test" workflow to use more modern mechanisms

Summary:
Depends on D19860. Ref T13222. Ref T10743. See PHI996.

Long ago, there were different types of feed stories. Over time, there was less and less need for this, and nowadays basically everything is a "transaction" feed story. Each story renders differently, but they're fundamentally all about transactions.

The Notification test controller still uses a custom type of feed story to send notifications. Move away from this, and…