Create virtual field

curl --request POST \
  --url https://api.axiom.co/v2/vfields \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "dataset": "<string>",
  "description": "<string>",
  "expression": "<string>",
  "name": "<string>",
  "type": "<string>",
  "unit": "<string>"
}'

{
  "dataset": "<string>",
  "description": "<string>",
  "expression": "<string>",
  "name": "<string>",
  "type": "<string>",
  "unit": "<string>",
  "id": "<string>"
}