Core config feature is not working as expected.

### Feature or problem description

I have been playing with the config and it looks like it is not working as it should.

Config is not properly strongly typed:

```
cfg interface{}
```

Config should provide interface for load and save where save and load triggered from the plugin will actually execute top level save and load functions and return proper results. Go doesn't support generics but what we really need to is to bridge specific load and save functions in plugin with host cli. If we can override plugin save methods and load methods on the host that will be all that is needed.

The current implementation is crashing for me when setting up in root and plugin with sample config on MergePluginCfg.