Drop dependency on secure_headers, fix response headers (#15712)

* Drop dependency on secure_headers, use always_write_cookie instead

* Fix cookies in Tor Hidden Services by moving configuration to application.rb

* Instead of setting always_write_cookie at boot, monkey-patch ActionDispatch

lib/action_dispatch/cookie_jar_extensions.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module ActionDispatch
+  module CookieJarExtensions
+    private
+
+    # Monkey-patch ActionDispatch to serve secure cookies to Tor Hidden Service
+    # users. Otherwise, ActionDispatch would drop the cookie over HTTP.
+    def write_cookie?(*)
+      request.headers['Host'].ends_with?('.onion') || super
+    end
+  end
+end
+
+ActionDispatch::Cookies::CookieJar.prepend(ActionDispatch::CookieJarExtensions)