Add the option to download all of the attachments present on one page at the same time

Currently there is no way for a user (Admin or regular user) to download all of the attachments belonging to one page at the same time. They have to download each file separately, and this becomes a chore when the page has many attachments.

There are some workarounds, but each one has a caveat to it:

• export the page as HTML then unzip and find the attachments in an attachment directory --> it's a bit complex for the average user to do
• use the snippet from https://snippets.xwiki.org/xwiki/bin/view/Extension/DownloadAttachments/ --> not useful for users who do not have Programming rights
• import and use the macro from https://extensions.xwiki.org/xwiki/bin/view/Extension/DownloadAttachments/ --> in my opinion, something similar should be part of the standard product.