appview/pages: add external link panel to issues

Signed-off-by: oppiliappan <[e-mail]>

appview/pages/templates/repo/issues/issue.html

···
               "Subject" $.Issue.AtUri
               "State" $.Issue.Labels) }}
       {{ template "repo/fragments/participants" $.Issue.Participants }}
+      {{ template "repo/fragments/externalLinkPanel" $.Issue.AtUri }}
     </div>
   </div>
 {{ end }}