Please note that the MQTT certificates are optional. If you have configured your MQTT broker (e.g. Mosquitto) to validate the client-certificates then these are needed, in any other case you can just connect as you normally would to your MQTT broker.
Please see the [integration.mqtt] and [integration.mqtt.client] configuration sections (Configuration - ChirpStack open-source LoRaWAN® Network Server documentation).
Other useful links: