curl --request POST \
  --url https://cloud.onyx.app/api/admin/tool/custom \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "name": "<string>",
  "description": "<string>",
  "definition": {},
  "custom_headers": [
    {
      "key": "<string>",
      "value": "<string>"
    }
  ],
  "passthrough_auth": true
}'

{
  "id": 123,
  "name": "<string>",
  "description": "<string>",
  "definition": {},
  "display_name": "<string>",
  "in_code_tool_id": "<string>",
  "custom_headers": [
    "<any>"
  ],
  "passthrough_auth": true
}