Use imei-imagemagick-7 DEB packages on ubuntu-20.04

[jnweiger]

WHAT Needs to be Documented?

Use of imei-imagemagick-7 DEB packages

A download repo with all needed *.deb packages can be one-click-generated using RUN.sh from https://github.com/jnweiger/imei-imagemagick Example: http://195.201.128.253/imei-imagemagick/repo/

WHERE Does This Need To Be Documented (Link)?

https://github.com/owncloud/docs/blob/master/modules/admin_manual/pages/installation/manual_installation/manual_imagick7.adoc

WHY Should This Change Be Made?

It's easier.

(Optional) What Type Of Content Change Is This?

• [ ] New Content Addition
• [ ] Old Content Deprecation
• [x] Existing Content Simplification
• [ ] Bug Fix to Existing Content