Split timeline_preview setting into more granular settings (#36338)

db/migrate/20251002140103_migrate_timeline_preview_setting.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class MigrateTimelinePreviewSetting < ActiveRecord::Migration[8.0]
+  class Setting < ApplicationRecord; end
+
+  def up
+    setting = Setting.find_by(var: 'timeline_preview')
+    return unless setting.present? && setting.attributes['value'].present?
+
+    value = YAML.safe_load(setting.attributes['value'], permitted_classes: [ActiveSupport::HashWithIndifferentAccess, Symbol])
+
+    Setting.upsert_all(
+      %w(local_live_feed_access remote_live_feed_access local_topic_feed_access remote_topic_feed_access).map do |var|
+        { var: var, value: value ? "--- public\n" : "--- authenticated\n" }
+      end,
+      unique_by: :var
+    )
+  end
+
+  def down; end
+end