Proposal: Add a --quiet or -y option for authgear init secrets

The use case is for local project setup, where database user and password are defined in `.env` and instead of supplying through command line we would use tools to overwrite the values instead.

Currently the workaround is
```
echo "" | docker run --rm -it -w "/work" -v "$PWD:/work" quay.io/theauthgear/authgear-server authgear init secrets
sed -i "s/postgres:postgres/$DB_USER:$DB_PASSWORD/g"
# Replace other values...
```

## Optional: Add default env for authgear init secrets
So that the following works:
```
docker run --rm -it -w "/work" -v "$PWD:/work" quay.io/theauthgear/authgear-server authgear init secrets -e DB_USER=postgres -e DB_PASSWORD=postgres -e DB_HOST=localhost -e REDIS_HOST=localhost
```

The name of these variables in the example are placeholders only.

I suppose the implementation would automatically work with `--env-file` as well.

Start by locating the `authgear init secrets` CLI entry point and inspect its option parsing and prompt/input handling. Clarify whether the required scope is only `--quiet`/`-y` or also environment and `--env-file` support; done means secrets initialization can use supplied values without interactive input.

Written by the indexing model from the issue text.