Manually Re-Initialize ElasticSearch

Depending on deployment of Querybook, manual re-initialization of indices in ElasticSearch might be needed when upgrading to new versions of Querybook.

This may happen for example when your web component is not started with querybook/scripts/bundled_docker_run_web script with --initdb option.

In such a cases, one has the following options how to initialize them manually:

In Docker based deployments, attach to web or worker component and run
```
python ./querybook/server/scripts/init_es.py
```

Locally, set following keys to proper values in querybook/config/querybook_config.yaml

FLASK_SECRET_KEY: ...
DATABASE_CONN: ...
REDIS_URL: ...
ELASTICSEARCH_HOST: ...

and run

PYTHONPATH=querybook/server python ./querybook/server/scripts/init_es.py