This is a quick component I whipped up to send notify notifications to an MQTT topic, since I had an existing notification infrastructure set up in Node-RED before migrating much of my automation over to Home Assistant, and wanted to be able to re-use it.
I was going to submit it to HA as part of the MQTT integration, but time pressures, alas, meant that I don’t have the time right now to learn the test platforms needed. If anyone else wants to take this code and merge it in there, you’re welcome to it.