Add utility to parse config and print out a key
Add utility to parse config and print out a key

Usage:

```
$ python -m synapse.config read server_name -c homeserver.yaml
localhost
```

TribeMedia/synapse,rzr/synapse,TribeMedia/synapse,matrix-org/synapse,iot-factory/synapse,matrix-org/synapse,TribeMedia/synapse,iot-factory/synapse,rzr/synapse,TribeMedia/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,rzr/synapse,rzr/synapse,matrix-org/synapse,TribeMedia/synapse,iot-factory/synapse,rzr/synapse,iot-factory/synapse,iot-factory/synapse