Migrate the micronaut-mqtt guides to use TestResources

[timyates]

The MQTT guides currently show setting up Mosquitto to handle MQTT connections.

We can use Test Resources instead.

ℹ️ This is currently blocked until a fix is added to the Test Resources plugin to check for both mqtt and mqttv5 in the dependencies.

Once unblocked, we should be able to:

1. Remove all the custom test classes that exclude MQTT
2. Remove mqtt.client.server-uri from the application.yml
3. Fix the guide to remove the manual mosquitto steps

We should manually work through the guide and ensure the paths in it are correct (app and cli directory prefixes)