Include read notifications in the tray API response

app/controllers/notifications/trays_controller.rb

@@ -1,9 +1,27 @@
 class Notifications::TraysController < ApplicationController
+  MAX_ENTRIES_LIMIT = 100
+
   def show
-    @notifications = Current.user.notifications.unread.preloaded.ordered.limit(100)
+    @notifications = unread_notifications
+    if include_unread?
+      @notifications += read_notifications
+    end
 
     # Invalidate on the whole set instead of the unread set since the max updated at in the unread set
     # can stay the same when reading old notifications.
     fresh_when Current.user.notifications
   end
+
+  private
+    def unread_notifications
+      Current.user.notifications.unread.preloaded.ordered.limit(MAX_ENTRIES_LIMIT)
+    end
+
+    def read_notifications
+      Current.user.notifications.read.preloaded.ordered.limit(MAX_ENTRIES_LIMIT)
+    end
+
+    def include_unread?
+      ActiveModel::Type::Boolean.new.cast(params[:include_unread])
+    end
 end