Change MQTT tuning procedure to a "custom-hiera"-based one

That way the configuration file won't be deleted when foreman-installer is run again and won't be needed to reload or restart services manually.

Author: pablomh

guides/common/modules/proc_increasing-host-limit-for-pull-based-rex-transport.adoc

@@ -3,32 +3,28 @@
 [id="Increasing_host_limit_for_pull_based_REX_transport_{context}"]
 = Increasing host limit for pull-based REX transport
 
-You can tune the `mosquitto` MQTT server and increase the number of hosts connected to it.
+You can tune the `mosquitto` MQTT server and increase the maximum number of hosts connected to it (by default it's 1014).
 
 .Procedure
-. Enable pull-based remote execution on your {ProjectServer} or {SmartProxyServer}:
+This example configures the `mosquitto` service on a {ProjectServer} or {SmartProxyServer} to handle 5000 content hosts.
+
+. Add the following to `/etc/foreman-installer/custom-hiera.yaml` to increase the default value:
 +
 [options="nowrap", subs="+quotes,verbatim,attributes"]
 ----
-# {foreman-installer} --foreman-proxy-plugin-remote-execution-script-mode pull-mqtt
+cat >>/etc/foreman-installer/custom-hiera.yaml <<EOF
+
+systemd::dropin_files:
+  limits.conf:
+    unit: mosquitto.service
+    content: "[Service]\nLimitNOFILE=5000\n"
+EOF
 ----
-+
-Note that your {ProjectServer} or {SmartProxyServer} can only use one transport mode, either SSH or MQTT.
-. Create a config file to increase the default number of hosts accepted by the MQTT service:
+. Enable pull-based remote execution:
 +
 [options="nowrap", subs="+quotes,verbatim,attributes"]
 ----
-cat >/etc/systemd/system/mosquitto.service.d/limits.conf <<__EOF__
-[Service]
-LimitNOFILE=5000
-__EOF__
+# {foreman-installer} --foreman-proxy-plugin-remote-execution-script-mode pull-mqtt
 ----
 +
-This example sets the limit to allow the `mosquitto` service to handle 5000 hosts.
-. Apply your changes:
-+
-[options="nowrap", subs="+quotes,verbatim,attributes"]
-----
-# systemctl daemon-reload
-# systemctl restart mosquitto.service
-----
+Note that your {ProjectServer} or {SmartProxyServer} can only use one transport mode, either SSH or MQTT.