Bindings and mappings option when adding skill

## Summary

Brief explanation of the feature.

### Basic example

```js
.addSkill(BasicSkill, {
  'bindings' => {
    'product' => 'product.graphql'
  },
  'mappings' => {
    'product' => 'product.mapping'
  }
})
```
### Motivation

Why are we doing this? What use cases does it support? What is the expected outcome?
