DIVI: add lightbox to regular content images

divi-lightbox-snippet-for-functions.php

/* add .et_pb_lightbox_image clss to content images */
add_filter('the_content', 'divi_add_lightbox');
function divi_add_lightbox($content) {
       global $post;
       $pattern ="/<a(.*?)href=('|\")(.*?).(bmp|gif|jpeg|jpg|png)('|\")(.*?)>/i";
       $replacement = '<a$1href=$2$3.$4$5 class="et_pb_lightbox_image" title="'.$post->post_title.'"$6>';
       $content = preg_replace($pattern, $replacement, $content);
       return $content;
}