refactor(article-link): abstract anchor attributes for making article links formattable

layouts/partials/article-link/simple.html

@@ -26,11 +26,7 @@
 {{ end }}
 
 
-{{ with .Params.externalUrl }}
-<a class="{{ $articleClasses }}" href="{{ . }}" target="_blank" rel="external">
-  {{ else }}
-  <a class="{{ $articleClasses }}" href="{{ .RelPermalink }}">
-    {{ end }}
+<a class="{{ $articleClasses }}" {{ partial "article-link/_external-link.html" . | safeHTMLAttr }}>
     {{- with $.Params.images -}}
     {{- range first 6 . }}
     <meta property="og:image" content="{{ . | absURL }}" />{{ end -}}