Dynamic Deserialization and merging of JSON Attachment

Question

I have a requirement 2 merge old and newly created JSON attachment. There are no duplicates. The JSON have below format :

{
  "productConfigurationId": "a06cdeghijklmnoABC",
  "attributesByAttrDefId": {
    "a01cefgh000lmnoPQR": {
      "attributes": {
        "type": "Attribute__c"
      },
      "Product_Configuration__c": "a06cdeghijklmnoABC",
      "Id": null,
      "Name": "SetOfferIds",
      "Attribute_Definition__c": "a01cefgh000lmnoPQR",
      "Hidden__c": false,
      "Key__c": null
    },
    "a01cefgh000lmnoSTU": {
      "attributes": {
        "type": "Attribute__c"
      },
      "Product_Configuration__c": "a06cdeghijklmnoABC",
      "Id": null,
      "Name": "Customer External Threshold",
      "Attribute_Definition__c": "a01cefgh000lmnoSTU",
      "Hidden__c": false,
      "Key__c": null
    }
   },
  "attrFieldsByAttrDefId": {}
}

What is the correct approach to do this? How will the wrapper be structured for this.