Implement an xarray subclass or accessor for quantify dataset v2

Related to #187 (closed).

TODO:

• research requirements for extending/subclassing xarray Dataset/DataArray and document the resources/links with that information in this issue

• implement a basic prototype, e.g., attach the to_gridded_dataset as a method of this new object, and provide a notebook/branch with the prototyping result

  • Prototype by Pieter available over here #233 (comment 643437076).

• define the desired features of the new object for next release

  • An important consideration is to keep it compatible with "casting" to a pure xarray object

• Implement a validation method/function/class that validates a dataset as a valid Quantify dataset as specified in the specification (!224 (merged))

  • Decide if the action of to_gridded_dataset yields an invalid Quantify dataset.
  • Moved to #270

Partially blocked by #187 (closed) and !224 (merged), prototyping can already start.