Enable celery monitoring via leek and celery-exporter

### Description/Context
Enable monitoring of celery tasks via leek.


### Plan/Design

Add the following to the `main/settings_celery.py` file:
  ```
  CELERY_TASK_TRACK_STARTED = get_bool("CELERY_TASK_TRACK_STARTED", True)
  CELERY_TASK_SEND_SENT_EVENT = get_bool("CELERY_TASK_SEND_SENT_EVENT", True)
  ```
