FEATURE: Rename onboarding popups to user tips (#18826)

This commit also hides the new user tips for existing users.

app/serializers/site_serializer.rb

@@ -6,7 +6,7 @@ class SiteSerializer < ApplicationSerializer
     :default_archetype,
     :notification_types,
     :post_types,
-    :onboarding_popup_types,
+    :user_tips,
     :trust_levels,
     :groups,
     :filters,
@@ -104,12 +104,12 @@ class SiteSerializer < ApplicationSerializer
     Post.types
   end
 
-  def onboarding_popup_types
-    OnboardingPopup.types
+  def user_tips
+    User.user_tips
   end
 
-  def include_onboarding_popup_types?
-    SiteSetting.enable_onboarding_popups
+  def include_user_tips?
+    SiteSetting.enable_user_tips
   end
 
   def filters