Dynamic Option Creation

Up from version 2.2.x + 2.3.x it is possible to create missing product option values for the admin store on the fly. This means that it is NOT possible to create translations for the other stores other than the admin store itself. This is, because when creating option values dynamically, the option values taken from the column additional_attributes always has to be the values for the admin store. Translations can be done in the Magento backend or with the attribute import. To enable this, additional frontend input callbacks have to be registered in the configuration file, for the add-update as well as the replace operations. The subject configuration should look like this

"subjects" : [
    "id" : "import_product.subject.bunch",
    "identifier" : "files",
    "file-resolver": {
      "prefix": "product-import"
    "observers" : [ ... ],
    "callbacks" : [ ... ],
    "params" : [ ... ],
    "frontend-input-callbacks": [
        "select": [
        "multiselect": [