[d8 advagg] add support for immutable cache control header

[pricejn2]

provision/http/Provision/Config/Nginx/Inc/vhost_include.tpl.php

Line 723 in 40b45d0

### Advagg_css and Advagg_js support.

Per https://git.drupalcode.org/project/advagg/blob/8.x-4.x/README.md#cache-control-immutable this is a relatively small addition.

   location ~ ^/sites/.*/files/(css|js)/optimized {
     add_header Cache-Control 'public, max-age=31536000, immutable';
   }