Create warning alerts to calculate message size

## What?
Be able to warn users if certain thresholds of license usage are reached. Make this a configurable option to warn the administrator by mail if 75% / 90% / 95% license usage is reached.

## Why?
Customers need to actively check the license/traffic page or ingest the value from the API to a metric system. For some customers suddenly - out of message sizing - the system stops working and it might break because the limits on disk are reached within hours if archiving/index rotation does not work anymore.

`[z#843460]