Change parameter http.headers.additional to use a dynamic value

[liviacirnu]

Hi! We have a use case where we want to use the parameter http.headers.additional use a changing value.
Example: Key:$Value1, where Value1 is coming from a field in the Kafka message value. We would like to send a PR to make this adjustment. How quickly can it be approved? Could you guide us with this process please :)

We found an old request about a similar feature over here: #30.