Adapt histogram endpoint to embed the CSV into a JSON format

Currently, the endpoint for the histogram of the data statistics returns the data in json or csv format. The UI needs the CSV for the plots however if we want to use the resthook useResource needs json. The idea is to add a new format json_csv that encapsulates the csv into json.

By having a csv_json we can use the useResource rest-hook and take advantage of the cache: E-DataPortal#547 (closed)