Redirect from Web tag timeline to public tag timeline if not signed in (#6633)

This is also implemented in Pawoo:
https://github.com/pixiv/mastodon/commit/ceafdbd1bbf30fe20a2a814df0f8cae429a4e9db

app/controllers/home_controller.rb

@@ -34,7 +34,8 @@ class HomeController < ApplicationController
       end
     end
 
-    redirect_to(default_redirect_path)
+    matches = request.path.match(%r{\A/web/timelines/tag/(?<tag>.+)\z})
+    redirect_to(matches ? tag_path(CGI.unescape(matches[:tag])) : default_redirect_path)
   end
 
   def set_initial_state_json