added elrepo element

Change-Id: I7bc144afa96f45122857ff634c8c19c1fd759450

diskimage_builder/elements/elrepo/README.rst

@@ -0,0 +1,10 @@
+======
+ELRepo
+======
+
+Enables ELRepo, a community based repository for Enterprise Linux Packages with a focus
+on drivers for hardware such as network interface cards. RHEL/CentOS versions pior to 8
+are not supported.
+
+* ``DIB_ELREPO_KERNEL`` Whether elrepo-kernel repository containing kernel-ml packages
+  should be enabled (1) or disabled. Default is disabled (0).

diskimage_builder/elements/elrepo/pre-install.d/01-elrepo

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+#!/bin/bash
+
+if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
+    set -x
+fi
+
+set -euo pipefail
+
+case "$DISTRO_NAME" in
+    centos* | rhel* | rocky*)
+    dnf install -y elrepo-release.noarch
+    if [ ${DIB_ELREPO_KERNEL:-0} -eq 1 ]; then
+        rpm -q dnf-plugins-core || dnf install -y dnf-plugins-core
+        dnf config-manager --set-enabled "elrepo-kernel"
+    fi
+    ;;
+    *)
+    echo "Distro \"$DISTRO_NAME\" is not supported"
+    exit 1
+    ;;
+esac
+exit 0

releasenotes/notes/elrepo-element-85b32f6f496234d7.yaml

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+---
+features:
+  - |
+    Added ELRepo element.