[Data Quality] General Score KPI calculation

/cc @imurua , @jordiarjona, @marijotecnalia

Hi @arkats ,

A new property called "rules_overall_score" should be added to the current JSON returned by the QE, so that the JSON would look like this:

{
    "rules_overall_score": 97.00
    "UDRG": [ ...],
    "dataset_id": "83cc2b24-a1b2-40b0-9190-aa88c2f57721",
    "profiling": [ ...],
    "timestamp": "2025-07-16 10:41:56"
}

The value of this property should be calculated by the QE as the arithmetic mean of all the values present in the "dqv_value" property inside the UDRG list.