add placeholder in metrics for historical 30 day diff
add placeholder in metrics for historical 30 day diff

added as "historical_values": {"raw_diff_30_days": 2}

Impactstory/total-impact-core,Impactstory/total-impact-core,Impactstory/total-impact-core,total-impact/total-impact-core,Impactstory/total-impact-core,total-impact/total-impact-core,total-impact/total-impact-core,total-impact/total-impact-core