FEATURE: Implement new onboarding popups (#18362)

This commit introduces a new framework for building user tutorials as
popups using the Tippy JS library. Currently, the new framework is used
to replace the old notification spotlight and tips and show a new one
related to the topic timeline.

All popups follow the same structure and have a title, a description and
two buttons for either dismissing just the current tip or all of them
at once.

The state of all seen popups is stored in a user option. Updating
skip_new_user_tips will automatically update the list of seen popups
accordingly.

db/migrate/20220923212549_add_seen_popups_to_user_options.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddSeenPopupsToUserOptions < ActiveRecord::Migration[7.0]
+  def change
+    add_column :user_options, :seen_popups, :integer, array: true
+  end
+end