Update documentation on configuring announcement banner to indicate new Jira experience does not have this feature

Creating this documentation update request based on this comment: https://jira.atlassian.com/browse/JRACLOUD-67563?focusedCommentId=1686903&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-1686903

As this user noted, the current documentation for Jira Cloud on configuring an announcement banner does not take into consideration that this feature currently doesn't exist in the New Jira experience.
It would help if there were a banner or a warning at the top of this page to explain that for the time being this feature does not exist in the new experience. And that there is a suggestion request to add this in https://jira.atlassian.com/browse/JRACLOUD-67563
And in the meantime if you need to use this feature in Jira Cloud, it appears you would need disable the new experience.