Add Matrix notifications when a product details update is executed/completed

[gabrielBusta]

Triggering a product details repository update (sending a message to the pulse queue) works most of the time. However, when it doesn't work, it can, and often does, fail silently if the message is somehow dropped.

ShipIt has a mechanism for sending messages to the release driver's Matrix channels. We could probably send a Matrix notification when the worker picks up an update or maybe when it finishes pushing it. This way, if product_details.py is suspiciously quiet post-version bump, we know we need to manually trigger a rebuild from the UI.