Allow admins to disable Unsplash integration used for page header images

Issue Summary

The Add header image feature in page edit mode is currently dependent on Unsplash, which is a third-party provider. However, it cannot be disabled at the moment. To ensure that Confluence is not affected in case Unsplash is compromised, Confluence admins should be given the option to disable this feature at the site level.

Workaround

Currently, there is no known workaround for this behavior. A workaround will be added here when available