Modify form-data Request body - Add new Key-Value

[adithyaseelam]

We have an use case where were receive form-data payload with multiple key value pairs. I need extract value from one key, create an json object and assign it to new Key. 
New payload should have the existing values along with the new one.

Example:

From the above screen shot. I need to extract value of Sample Key which is an json object and create a new Key Sample2 in the below json format. 

{                
"Trace-Id": "abc123ABC",
"Time": "{client.received.end.timestamp}",
"Payload": ["{Sample Value}"]
}  

My Final req going to target system should look like below snapshot.