Notify sysadmins via email when license user limit is reached

Problem Definition

When the license user limit is reached, a warning is displayed in the UI showing that a 24 grace hour period has started. Sometimes the user limit may be reached whilst nobody is actively using Bitbucket, e.g. changes to an external directory over a weekend. This can result in the grace period finishing before sysadmins are aware of the issue

Suggested Solution

Email sysadmins a proactive notification when the user limit is reached