Add AlmaLinux as a supported os for self managed installations

Proposal

Add AlmaLinux as a supported os for self-managed installations.

Currently, when you try to install gitlab, it says:

Detected operating system as almalinux/8.
Checking for curl...
Detected curl...
Downloading repository file: https://packages.gitlab.com/install/repositories/gitlab/gitlab-ee/config_file.repo?os=almalinux&dist=8&source=script
curl: (22) The requested URL returned error: 404 Not Found


Unable to download repo config from: https://packages.gitlab.com/install/repositories/gitlab/gitlab-ee/config_file.repo?os=almalinux&dist=8&source=script

This usually happens if your operating system is not supported by 
packagecloud.io, or this script's OS detection failed.

You can override the OS detection by setting os= and dist= prior to running this script.
You can find a list of supported OSes and distributions on our website: https://packages.gitlab.com/docs#os_distro_version

For example, to force CentOS 6: os=el dist=6 ./script.sh

If you are running a supported OS, please email support@packagecloud.io and report this.

It would be nice to have alma as a supported os because it aims to replace CentOS (which has since become CentOS Stream) as a binary compatible free alternative to RHEL.