Feat/mqtt integration

[jona159]

This PR includes:

• db schema for integrations and relations (based on PR feat: add integrations #462)
• mqtt client to talk to the mqtt-microservice
• endpoints to get mqtt status of devices
• internal endpoint to ingest measurements via mqtt

To test this branch with the mqtt service, clone the mqtt service repo and create the .env file.
Run npm run dev to run the service.
On the api side create a test device with sensors and add an mqtt integration, e.g. like:

const [integration] = await client
		.insert(mqttIntegration)
		.values({
			enabled: true,
			url: 'mqtt://test.mosquitto.org', // Public test broker
			topic: `opensensemap/test/${testDevice.id}`,
			messageFormat: 'json',
			decodeOptions: null,
			connectionOptions: {
				keepalive: 60,
				connectTimeout: 5000,
			},
			deviceId: testDevice.id,
		})
		.returning()

await client.insert(deviceToIntegrations).values({
		deviceId: testDevice.id,
		mqttIntegrationId: integration.id,
	})

Afterwards install mosquitto, e.g. on ubuntu:
sudo apt install mosquitto mosquitto-clients -y

and run e.g.:

mosquitto_pub -h test.mosquitto.org \
  -t "opensensemap/test/_DEVICE_ID" \
  -m '{"SENSOR_ID_1": 3.5, "SENSOR_ID_2": 95}'

The logs should indicate if it worked and the measurements should be saved to the database.