Support extendable output types as an option instead of simple scalars

Currently, the fields of interest resolve to a certain Scalar type.
```gql
type Window {
position: Int
}
```

This implies that the output type cannot be extended to contain custom metadata that might be useful in some cases. For example: frequency, accuracy, confidence, timestamp, etc.

To enable that the output should be more than the scalar itself. It can be named `Extended`, `Property`, or similar to imply the capability to extend.

```gql
type Window {
position: IntProperty
}
```

Defined in `S2DM`
```gql
type IntProperty {
value: Int
timestamp: Timestamp
... # Empty and to be extended by the particular needs of the user
}
```

Extended in the domain model repository that follows `S2DM`
```gql
extend type IntProperty {
confidence: Int
accuracy: Float
...
}
```