collectd: Add write_prometheus uci config

Included with default options used by collectd

Signed-off-by: Xiao Yu <me@xyu.io>

utils/collectd/files/collectd.uci

@@ -230,3 +230,9 @@ config globals 'globals'
 #	option blocktype 'Subscribe'
 #	option Host 'localhost'
 #	option Topic 'collectd/#'
+
+#config plugin 'write_prometheus'
+#	option enable '0'
+#	option Host '0.0.0.0'
+#	option Port '9103'
+#	option StalenessDelta '300'

utils/collectd/files/usr/share/collectd/plugin/write_prometheus.json

@@ -0,0 +1,7 @@
+{
+	"string": [
+		"Host",
+		"Port",
+		"StalenessDelta"
+	]
+}