recursively flatten a nested jsonb in postgres without unknown depth and unknown key fields

How can I recursively flatten a nested jsonb in postgres which I don't know the depth and the field at each depth? (see example below)

A postgressql query to do the flattening would be much apreciated

    {
       "xx": "",
       "xx": "",
       "form": "xxx",
       "type": "",
       "content_type": "xxx",
       "reported_date": ,
       "contact": {
           "imported_date": "",
           "name": "",
           "phone": "",
           "alternate_phone": "",
           "specialization": "",
           "type": "",
           "reported_date": ,
           "parent": {
               "_id": "xxx",
               "_rev": "xxx",
               "parent": "",
               "type": "xxx" 
               } 
        }
    }

I have searched in stack overflow but they only consider jsonb's which have a single depth and the keys are already known before