fix: add rel option to external links in content (#1853)

* #1853: XSS attack fix by adding rel noferrer or rel noopen to _blank target external links

* fix: relAttributeExternalLink noopener

Co-authored-by: danallendds <daniel.allen@friends.dds.mil>
Co-authored-by: Nicolas Giard <github@ngpixel.com>

server/modules/rendering/html-core/renderer.js

@@ -115,6 +115,7 @@ module.exports = {
         $(elm).addClass(`is-external-link`)
         if (this.config.openExternalLinkNewTab) {
           $(elm).attr('target', '_blank')
+          $(elm).attr('rel', this.config.relAttributeExternalLink)
         }
       }