http-kafka fetch binding returns malformed JSON when the payload is large

[vordimous]

Describe the bug
When fetching larger payloads the resulting JSON would have random commas (,) placed in the text causing failed JSON parsing. Checking data ingress and on Kafka looks to be correct JSON.

To Reproduce
Steps to reproduce the behavior:

1. checkout zilla-demos/taxi@mqtt-load-test
2. start the demo with startup.sh
3. once the demo has started, edit the "RANGE_END": 300, value in the taxi/grpc/service/*_load_test_*.json files meaning
4. restart the taxi-service: docker-compose -p zilla-taxi-demo restart taxi-service.
5. the metric stream_active_received{namespace="zilla-taxi-demo",binding="mqtt_server"} should now be 900
6. The UI will now throw errors like Unexpected token ',', ...", "icon": ,"airport_"... is not valid JSON
7. I checked the JSON in the Kafka payloads and didn't find any extra commas: kcat -C -b localhost:9092 -t taxi-messages -J -u | jq .payload >> out.json

Desktop (please complete the following information):

• OS: MacOS
• Zilla: 0.9.55