Setting LOG_FORMAT: json does not write stack traces to logs

[matthewelwell]

To reproduce:

1. Spin up a local instance of Flagsmith and set the environment variable LOG_FORMAT: json
2. Trigger an internal server error (e.g. try to send an invite email without having SMTP configured)

Expected behaviour:

A stack trace is printed to the logs

Actual behaviour:

No stack trace is printed, only the JSON formatted log message as per the below.

{"levelname": "ERROR", "message": "Internal Server Error: /api/v1/organisations/2/invite/", "timestamp": "2024-05-29 08:54:17", "logger_name": "django.request", "process_id": 34, "thread_name": "ThreadPoolExecutor-1_0"}