🔒️(nginx) manage Content-Security-Policy in nginx config

The media route is managed by nginx. On this route we want to add the
Content-Security-Header to forbid fetching any resources.
See : https://content-security-policy.com/

docker/files/etc/nginx/conf.d/default.conf

@@ -68,6 +68,8 @@ server {
         # Get resource from Minio
         proxy_pass http://minio:9000/impress-media-storage/;
         proxy_set_header Host minio:9000;
+
+        add_header Content-Security-Policy "default-src 'none'" always;
     }
 
     location /media-auth {