Draft: adding link tags with alternate attribute in head section, for rss autodiscovery

Summary

I tried to write this patch for #1307 but isn't working inside development environment, because link.href is generated as relative link. Any hint how to pass integration test with APIs?

<link data-react-helmet="true" href="/users/tassoman/feed.atom" rel="alternate" type="application/rss+xml">
<link data-react-helmet="true" href="/@tassoman" rel="alternate" type="application/activity+json">