add plugins/emqttd_plugin_template

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "plugins/emqttd_dashboard"]
 	path = plugins/emqttd_dashboard
 	url = https://github.com/emqtt/emqttd_dashboard.git
+[submodule "plugins/emqttd_plugin_template"]
+	path = plugins/emqttd_plugin_template
+	url = https://github.com/emqtt/emqttd_plugin_template.git

plugins/emqttd_plugin_template

@@ -0,0 +1 @@
+Subproject commit d10ee3dcdaf4e7d17f50ed0745c39628a96678e2