Preserve rel=me on links in rich text

Fixes #3859

config/initializers/sanitize.rb

@@ -1,11 +1,16 @@
 Sanitize::Config::OSM = Sanitize::Config.merge(
   Sanitize::Config::RELAXED,
   :elements => Sanitize::Config::RELAXED[:elements] - %w[div style],
-  :add_attributes => { "a" => { "rel" => "nofollow noopener noreferrer" } },
   :remove_contents => %w[script style],
   :transformers => lambda do |env|
     env[:node].remove_class
     env[:node].kwattr_remove("style", nil)
     env[:node].add_class("table table-sm w-auto") if env[:node_name] == "table"
+
+    if env[:node_name] == "a"
+      rel = env[:node]["rel"] || ""
+
+      env[:node]["rel"] = rel.split.select { |r| r == "me" }.append("nofollow", "noopener", "noreferrer").sort.join(" ")
+    end
   end
 )