Add metadata to data being sent to API endpoint in JSON dump registration backend

[viktorvanwijk]

Follow-up of #4908

Suggestion is to add metadata to the data being sent. In the JSON dump configuration options, any variable (component, user-defined, or static) can be selected to add to this metadata, with several pre-selected variables such as:

• Form name (form_name)
• Form ID (form_id)
• Submission ID (submission_id)
• Now (now)
• Authentication type (auth_type)
• Others...?

Example

An example form with the following configuration:

• Authentication via DigiD, capturing a BSN
• First form step with text fields firstName and lastName
• Second form step with a user upload attachment

Should lead to a JSON object being sent with the shape:

{
    "metadata":
    {
        "form_name": "Form 1",
        "form_id": "b78d063c-e249-4217-99e3-eaf3cf1fd590",
        "submission_id": "6e2fd868-ba06-4faf-a8ec-c4d27d55cea8"
        "now": "2025-01-10T15:28:00+01:00",
        "auth_type": "bsn",
    }
    "metadata_schema":
    {
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "type": "object",
        "properties":
        {
            "form_name":
            {
                "title": "Form name",
                "type": "string"
            }
            "form_id":
            {
                "title": "Form identifier",
                "type": "string",
                "format": "uuid"
            }
            "submission_id":
            {
                "title": "Submission identifier",
                "description": "UUID of the submission",
                "type": "string",
                "format": "uuid",
            }
            "now":
            {
                "title": "Current date time",
                "type": "string",
                "format": "date-time"
            },
            "auth_type": 
            {
                  "title": "Authentication type",
                  "type": "string",
                  "enum": ["bsn", "kvk", "pseudo", "employee_id"]
            },
    }
    "values":
    {
        "auth_bsn": "123456782",
        "firstName": "Donnie",
        "lastName": "Darko",
        "attachment": "<base64 encoded data>"
    },
    "values_schema":
    {
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "type": "object",
        "properties":
        {
            "auth_bsn":
            {
                "type": "string",
                "pattern": "^\\d{9}$"
            },
            "firstName":
            {
                "type": "string"
            },
            "lastName":
            {
                "type": "string"
            },
            "attachment":
            {
                "type": "string",
                "contentEncoding": "base64"
            }
        },
        "required":
        [
            "auth_bsn",
            "firstName",
            "lastName"
        ],
        "additionalProperties": false
    }
}