If fnReturn.body is CloudEvent, we should return CloudEvent's data as response body instead of the whole CloudEvent as response body

When we define the response headers in StructuredReturn, the whole CloudEvent is returned as response body instead of the CloudEvent's data.

curl -X POST -d '{"hello": "world"}' \
  -H'Content-type: application/json' \
    -H 'Ce-Id: asdadadsada' \
    -H 'Ce-type: user-request' \
    -H 'Ce-specversion: 1.0' \
    -H 'Ce-correlationid: 123' \
    -H 'Ce-mode: SYNC' \
    -H 'Ce-Source: nodejs' \
    http://localhost:8080

expected: {"hello":"world"}

actual: {"id":"asdadadsada","time":"2023-04-10T03:50:12.135Z","type":"user-request","source":"nodejs","specversion":"1.0","datacontenttype":"application/json","data":{"hello":"world"},"correlationid":"123","mode":"SYNC"}

Start by reproducing the issue with the provided curl request and trace the StructuredReturn response handling in the JavaScript runtime. Done means that when fnReturn.body is a CloudEvent and response headers are defined, the HTTP response body contains the CloudEvent's data rather than the full CloudEvent.