Add example plugin with documentation

scripts/plugins/example/alert_definitions/alert_example.lua

@@ -0,0 +1,28 @@
+--
+-- (C) 2019 - ntop.org
+--
+
+-- This file defines a new alert, with key "alert_example" (the file name)
+-- Alerts can be triggered by the user scripts located into the "user_scripts"
+-- directory of the plugin.
+
+return {
+  -- The unique alert ID. Currently used/available IDs can be reviewed by visiting
+  -- http://127.0.0.1:3000/lua/defs_overview.lua .
+  -- Third party users can safely use the dedicated IDs in range 59-63 .
+  alert_id = 59,
+
+  -- The name associated to this alert. Localized strings are defined in
+  -- example/locales/en.lua
+  i18n_title = "example.alert_title",
+
+  -- An icon (css class name) associated to this alert. ntopng supports icons
+  -- from https://fontawesome.com .
+  icon = "fa-exclamation",
+
+  -- An optional alert message to show when the alert is triggered. For flow
+  -- alerts, however, the alert message is defined into the status associated
+  -- to the alert, which is example/status_definitions/status_example.lua for
+  -- this plugin.
+  i18n_description = "example.alert_description",
+}