feat(config)!: Move mqtt module to actual separate module

The automation:mqtt module now gets loaded in a similar way as the
automation:devices and automation:utils modules.
This leads to a breaking change where instantiating a new mqtt client
the device manager needs to be explicitly passed in.

config.lua

@@ -21,7 +21,7 @@ local fulfillment = {
 	openid_url = "https://login.huizinga.dev/api/oidc",
 }
 
-local mqtt_client = require("automation:mqtt").new({
+local mqtt_client = require("automation:mqtt").new(device_manager, {
 	host = ((host == "zeus" or host == "hephaestus") and "olympus.lan.huizinga.dev") or "mosquitto",
 	port = 8883,
 	client_name = "automation-" .. host,