Remove CentOS 8 support

Reason: CentOS 8 reached its EOL and was also removed from nicadist.

CentOS 7 remains the default toolbox environment image.

We will supported at least one more image - Centos 8 Stream, Centos 9 Stream, or some other (AlmaLinux 9, RockyLinux).
It will likely will be the same OS, which will be installed on the cluster, after they decide to move away from CentOS 7.
So far the decision was not made yet.

Edited Jul 14, 2022 by Slavomir Hnatic

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information