Switch ELN to a native container

Relates: fedora-eln/eln#164
Fixes: #1238

mock-core-configs/etc/mock/templates/fedora-eln.tpl

@@ -13,7 +13,10 @@ config_opts['chroot_setup_cmd'] = 'install bash bzip2 coreutils cpio diffutils f
 config_opts['dist'] = 'eln'  # only useful for --resultdir variable subst
 config_opts['extra_chroot_dirs'] = [ '/run/lock', ]
 config_opts['package_manager'] = 'dnf'
-config_opts['bootstrap_image'] = 'fedora:latest'
+
+# Per https://github.com/fedora-eln/eln/issues/164 updated up to 4 times a day.
+# Docs: https://docs.fedoraproject.org/en-US/eln/deliverables/#_container_image
+config_opts['bootstrap_image'] = 'quay.io/fedoraci/fedora:eln'
 
 config_opts['dnf.conf'] = """
 [main]

releng/release-notes-next/fedora-eln-image.config

@@ -0,0 +1,5 @@
+Previous versions of mock-core-configs referenced `fedora:latest` bootstrap
+images for `fedora-rawhide-ARCH` chroots, which led to [package
+incompatibilities][issue#1238].  Turns out ELN folks already provide a ["native"
+ELN image](https://docs.fedoraproject.org/en-US/eln/deliverables/#_container_image)
+so the new configs have switched to use that.