Set kafka message key as one of the fields from document

Hi,

Have the following message

{
  "_id": {
    "_data": "8264140F5E000000012B022C0100296E5A1004EA22F9595AEB4D7BB559262ED2C26B58463C5F6964003C31353632643837632D613062612D343638632D626330352D34326166323264343733636323464F4C4445522335396136613231332D306230642D346164322D626630622D336635363966383137303137000004"
  },
  "clusterTime": 1679036254000,
  "documentKey": {
    "_id": "59a6a213-0b0d-4ad2-bf0b-3f569f817017"
  },
  "fullDocument": {
    "_id": "59a6a213-0b0d-4ad2-bf0b-3f569f817017",
    "accId": "1562d87c-a0ba-468c-bc05-42af22d473cc",
    "refId": "1562d87c-a0ba-468c-bc05-42af22d473cc"
  },
  "ns": {
    "coll": "employee",
    "db": "accounts"
  },
  "operationType": "insert",
  "wallTime": 1679036254562
}

Please let me know how to configure/set “fullDocument.refId” as message key?
BTW, we require “publish.full.document.only” as false inorder to get other metadata.