Several configurations in one file

I would like to be able to create several configurations in `.protokaf.yaml:`
Something like that:
```yaml
profiles:
  local:
    debug: true
    broker: 0.0.0.0:9092

  stage:
    debug: true
    broker: stage.host:9093
    kafka-auth-dsn: "SCRAM-SHA-256:admin:secret"
```

And using it that way:
```bash
$ protokaf consume HelloRequest -P stage ...
```
