Propose interface for datasets

[FranckCo]

In order to expand the support of dataset, we need an abstract definition of the dataset type.

[romaintailhurat]

Working on it: https://github.com/InseeFr/VTL-Tools/pull/49

[romaintailhurat]

Because we don't have abstraction like Typescript interface, it's hard to reify our intended "outer" dataset representation.

What would be the best way to document and represent it in the code ?

Our current proposition is an object of this shape:

{
  "ds": {
    // Holds the dataset structure information
    "dataStructure": {
      "col_1": {
        "name": "col_1",
        "role": "MEASURE"
      }
    },
    // Holds the columns, named and stored as arrays
    "dataPoints": {
      "col_1": [
        1,
        2,
        3
      ]
    }
  }
}