AWS Cloudwatch setup - initial_position parameter in the new logs agent

In older version of AWS Cloudwatch agent, there was a parameter for initial_position. But I am not able to find it in the new Cloudwatch agent. Older version of CloudWatch

initial_position = start_of_file

But I am not able to find the same anywhere in the new documentation. Please help in pointing to the parameter for this.

collect_list :[{
"file_path": "/var/log/nginx/access.log",
"log_group_name": "GroupName",
"log_stream_name": "nginxAccessLogStream",
"timezone": "UTC"
}]

Edit: Found Logs Input Plugin. Field: from_beginning

https://github.com/aws/amazon-cloudwatch-agent/tree/f870550f94a822f3eceaea0ecb2efdeabe961e5c/plugins/inputs/logfile

But adding it is not running the plugin.