Put search index process into background queue

[leonholub]

To reduce response times when saving models to the database the elasticsearch index should be updated in a background process and not in the save method.
This would require a celery task queue with a background task.

• set up redis
• add celery to django project
• add background task
• add possibility to track task status

[rafa-munoz]

There was some progress from Leon. An extract from my conversation with him:

He has created Celery Tasks for the Index and Delete processes and has tested locally.
Almost everything works, but there is still a problem. In the Indicator model comes the error:

is not JSON serializable

Aside from that it goes well with the queue. The other models were not tested.

I think there should be a way to make the models json serializable to put them in the queue.

Branch:
https://github.com/toladata/TolaActivity/tree/search-index-queue