Address more connector metadata schema feedback (#1007)

- Allow for parameterized tokens such as {assetName} and {namespace} in
the default MQTT topic + default dss key, + default storage path
- Un-nest the "supportedModeling" types
  - For instance:
  
```
{
    "supportedModeling": {
        "datasets": {
            "supportedModeling": {
                  "datapoints": {...}
             }
        }
    }
}
```

becomes

```
{
    "datasets": {
        "datapoints": {...}
    }
}
```

Author: timtay-microsoft