http > https

server {
  listen 80;
  server_name {{ server_name }};
  return 301 https://$server_name$request_uri;
}

server {
  server_name www.{{ server_name }};
  return 301 https://{{ server_name }}$request_uri;
}

server {
  listen 443 etc...

the above does all redirects to https://domainname. to redirect everything to https://www. do the following:

change both return 301 https://$server_name$request_uri; to return 301 https://www.$server_name$request_uri;

change server_name www.{{ server_name }}; to server_name {{ server_name }};