Create variant

curl --request POST \
  --url https://api.us.poly.ai/v1/agents/{agentId}/branches/{branchId}/variants \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "name": "<string>",
  "attributeValues": {
    "values": {}
  },
  "isDefault": true
}
'

{
  "id": "<string>",
  "name": "<string>",
  "isDefault": true,
  "attributeValues": {
    "values": {}
  }
}