Basic deployment does not work (datapusher asks for an undocumented API key)

Hi @kowh-ai , I tried to deploy CKAN using docker compose using the most regular workflow:

1. git clone this repo
2. Rename the `.env.sample` to `.env`
3. `docker compose up`
4. All containers starts and are healthy, apart from `ckan` which is unhealthy with the following error message in its logs:

```
ckan | raise Exception(
ckan | Exception: Config option `ckan.datapusher.api_token` must be set to use the DataPusher.
ckan | unable to load app 0 (mountpoint='') (callable not found or import error)
ckan | *** no app loaded. going in full dynamic mode ***
```

Unfortunately I could not find any documentation about the "DataPusher" in this repo: https://github.com/ckan/ckan-docker#9-datastore-and-datapusher

I would guess we need to pass some kind of API token to an env variable, but no idea what this env variable could be.

Would it be possible to know what is this variable? And what should we feed it to get ckan running standalone?