collectd: add logfile plugin definitions

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

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

@@ -0,0 +1,9 @@
+{
+	"string": [
+		"LogLevel",
+		"File"
+	],
+	"bool": [
+		"Timestamp"
+	]
+}