Resolve "Information on backup compression & encryption"

Merged Thom requested to merge thom/ispconfig3:5705-backup-information into stable-3.1

The removed text can/should be added to the manual.

I left the error for missing utils in the template, but changed the text so the user is aware that (and why) he/she can't use the not installed formats. I think we should add the required packages to the perfect server tutorials (also for the current debian 10 and centos 7 tutorial) and put a note in the release notes about it.

Closes #5705 (closed)

Edited by Thom

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