Documentation of Notifications

Under `Session management` -> `Desktop settings` there is a Notifications section which references `Cluster Settings`:


Documentation of [Desktop settings](https://docs.aws.amazon.com/res/latest/ug/desktop-settings.html) doesn't include Notifications and I can't find any reference to `Cluster Settings` in the UI or the docs.

Start with the linked Desktop settings documentation page and the Session management → Desktop settings area in the RES UI. Compare the documented sections with the Notifications section shown in the issue, investigate the Cluster Settings reference, and update the documentation so the relevant notification behavior and terminology are accurately covered.

Written by the indexing model from the issue text.