feat(install): provide EPEL repo configuration for `Amazon Linux-2`

syslog_ng/package/install.sls

 {%- set tplroot = tpldir.split('/')[0] %}
 {%- from tplroot ~ "/map.jinja" import syslog_ng with context %}
 
+{#- Simulating `grains.osfinger`, which is avoided since not available in all distros #}
+{%- if [grains.os, grains.osrelease] == ['Amazon', '2'] %}
+syslog_ng/package/repo:
+  pkgrepo.managed:
+    - name: epel
+    - humanname: Extra Packages for Enterprise Linux 7 - $basearch
+    - mirrorlist: https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch
+    - enabled: 1
+    - gpgcheck: 1
+    - gpgkey: https://dl.fedoraproject.org/pub/epel/RPM-GPG-KEY-EPEL-7
+    - failovermethod: priority
+    - require_in:
+      - pkg: syslog_ng/package/install
+{%- endif %}
+
 syslog_ng/package/install:
   pkg.installed:
     - name: {{ syslog_ng.package }}