Change unauthenticated responses to be cached in REST API (#24348)

app/controllers/api/v1/instances_controller.rb

@@ -3,8 +3,10 @@
 class Api::V1::InstancesController < Api::BaseController
   skip_before_action :require_authenticated_user!, unless: :whitelist_mode?
 
+  vary_by ''
+
   def show
-    expires_in 3.minutes, public: true
+    cache_even_if_authenticated!
     render_with_cache json: InstancePresenter.new, serializer: REST::V1::InstanceSerializer, root: 'instance'
   end
 end