Add haproxy plugin for Debian

checkmk/debian/mk_haproxy.sls

+hsh_checkmk_install_haproxy_plugin:
+  file.managed:
+    - name: /usr/lib/check_mk_agent/plugins/mk_haproxy
+    - source: salt://checkmk/checkmk-files/mk_haproxy.freebsd
+    - user: root
+    - group: root
+    - mode: 755