app-metrics/prometheus: fix service script

Introduce the prometheus_args variable. Allow the continued use of
command_args in the script for now to avoid breaking systems, but
document that people should move to prometheus_args.
Also, sync most of the defaults with the systemd service.

Signed-off-by: William Hubbs <williamh@gentoo.org>

app-metrics/prometheus/files/prometheus.confd

@@ -1,2 +1,26 @@
-# arguments for Prometheus
-command_args=""
+# additional arguments for Prometheus
+#
+# command_args should not be set in this file. Instead, you should set
+# prometheus_args.
+#
+# The default settings are listed below.
+# If you are not changing these settings, you do
+# not need to include them in prometheus_args.
+#
+# To migrate from using command_args to prometheus_args, drop any of the
+# default settings below that you have set the same way then switch to
+# prometheus_args.
+# 
+# The new behavior is that prometheus_args will be appended to these
+# defaults allowing anything you add to override them.
+#
+#The default settings are:
+#
+# --web.enable-lifecycle
+# --config.file=/etc/prometheus/prometheus.yml
+# --storage.tsdb.path=/var/lib/prometheus/data
+# --web.console.templates=/etc/prometheus/consoles
+# --web.console.libraries=/etc/prometheus/console_libraries
+# --web.enable-admin-api 
+#
+prometheus_args=""

app-metrics/prometheus/files/prometheus.initd

@@ -9,7 +9,19 @@ group=${group:-${RC_SVCNAME}}
 command_user=${user}:${group}
 
 command="/usr/bin/prometheus"
+if [ -z "${command_args}" ]; then
+command_args="
+	--web.enable-lifecycle
+	--config.file=/etc/prometheus/prometheus.yml
+	--storage.tsdb.path=/var/lib/prometheus/data
+	--web.console.templates=/etc/prometheus/consoles
+	--web.console.libraries=/etc/prometheus/console_libraries
+	--web.listen-address=0.0.0.0:9090
+	--web.enable-admin-api 
+	${prometheus_args}"
+else
 command_args="${command_args:---config.file=/etc/prometheus/prometheus.yml --storage.tsdb.path=/var/lib/prometheus/data}"
+fi
 command_background="true"
 error_log=/var/log/${RC_SVCNAME}/${RC_SVCNAME}.log
 output_log=/var/log/${RC_SVCNAME}/${RC_SVCNAME}.log