Creates a referral link

curl --request POST \
  --url https://v2.firstpromoter.com/api/v2/affiliate/referral_links \
  --header 'Account-ID: <account-id>' \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "promoter_campaign_id": 123,
  "sub_id": "<string>",
  "name": "<string>",
  "url": "<string>"
}'

{
  "id": 123,
  "name": "<string>",
  "url": "<string>",
  "is_default": true,
  "source": "campaign",
  "sub_id": "<string>",
  "campaign": {
    "id": 123,
    "name": "<string>",
    "color": "<string>"
  }
}