feat: create exporters module (#364)

- upgrade node_exporter, bring managed under exporters module
- upgrade postgres_exporter, bring managed under exporters module
- add flag to cleanup previous iterations of exporters from prometheus module
- fix issues with vmclusster: replication + dedup

Reviewed-on: #364

modules/exporters/templates/node_exporter.service.erb

@@ -0,0 +1,15 @@
+[Unit]
+Description=Prometheus node_exporter
+Wants=network-online.target
+After=network-online.target
+
+[Service]
+User=<%= @user %>
+Group=<%= @group %>
+ExecStart=<%= @exec_path %>
+ExecReload=/bin/kill -HUP $MAINPID
+KillMode=process
+Restart=always
+
+[Install]
+WantedBy=multi-user.target