Log which server config is being used on startup

#### What is the problem you want to solve?

Trying to upgrade to `v0.18.0` and took a while until I realised it was using an older server config version since I had

```yaml
keys:
  fs:
    path: /xyz
```

#### How do you want to solve it?

Maybe it could log what server config version is being used and not only

```sh
Error: no admin identity specified
```
