[markuslf]

Adds linuxfabrik-release, the counterpart to epel-release for repo.linuxfabrik.ch (GitLab 001/project-big-picture #1257, #650 step 2.2).

What it does

• Installs the repository configuration (release channel enabled, testing configured but disabled) and the Linuxfabrik signing key (1017377FDD935D369CCD0C59F27988EC39D17A78).
• RPM: /etc/yum.repos.d/linuxfabrik.repo (EL, Fedora) or /etc/zypp/repos.d/linuxfabrik.repo (SLES/Leap), key in /etc/pki/rpm-gpg/, gpgcheck=1 and repo_gpgcheck=1. EL gets the major version at build time (EL 8 has no $releasever_major) and an epel-release style Requires on redhat-release of that major.
• DEB: deb822 /etc/apt/sources.list.d/linuxfabrik.sources with Signed-By: /usr/share/keyrings/linuxfabrik.gpg, testing stanza Enabled: no.
• Targets: RHEL 8-10, Fedora 44, SLES/Leap 15 and 16, Debian 12/13, Ubuntu 22.04-26.04. Debian 11 is out: its security pool returns 404.
• publish.sh keeps bootstrap links linuxfabrik-release-latest-<distro>.<ext> in the webroot (EPEL's epel-release-latest-10.noarch.rpm model) and replays releases oldest first. Usage is documented in the README.

The SUSE repository path is sle/<version>/ instead of sles/ from #1252: one path for SLES, SLED and openSUSE Leap, as the monitoring-plugins repository does today.

Fixes found on the way

• create-rpm.sh: pin %_topdir, SLES builds in /usr/src/packages otherwise; give SLES builds .sle15 / .sle16, since SLES has no %{dist} and both releases would share a file name.
• create-package.sh: PKG_SOURCE_DIR for packages without an upstream.
• publish.sh: gzip repository metadata; libdnf on Rocky 8 aborts on the zstd default of createrepo_c 1.x.

Tested

On fresh VMs cloned from the templates of all 11 targets (Leap 15.5/16.0 standing in for SLES) against a Rocky 10 test server set up like 001-p-repo51 (freight, Apache with TLS for repo.linuxfabrik.ch):

• bootstrap through the -latest- link, metadata refresh with signature checks, reinstall from the repository; glances from testing on Rocky 10, Fedora 44, Debian 13 and Ubuntu 24.04
• publish.sh against the real GitHub release glances-4.5.8-1 with real gh attestation verify
• negative: dnf rejects metadata signed with another key ("Bad GPG signature"), zypper skips a repository whose repomd.xml.asc does not match

Merging this changes packages/linuxfabrik-release/ and creates the prerelease linuxfabrik-release-1-1.