Merge branch 'support-rel-ugc' into 'develop'

Add support for `rel="ugc"`

Closes #1255

See merge request pleroma/pleroma!1679

config/config.exs

@@ -509,7 +509,7 @@ config :auto_linker,
     class: false,
     strip_prefix: false,
     new_window: false,
-    rel: false
+    rel: "ugc"
   ]
 
 config :pleroma, :ldap,

config/description.exs

@@ -1906,7 +1906,7 @@ config :pleroma, :config_description, [
         key: :rel,
         type: [:string, false],
         description: "override the rel attribute. false to clear",
-        suggestions: ["noopener noreferrer", false]
+        suggestions: ["ugc", "noopener noreferrer", false]
       },
       %{
         key: :new_window,