Add analytics event when cluster panics

In order to improve the stability of Data Center, we need to understand how often our customers run into Cluster Panics. We've added a analytics event that triggers during a Cluster Panic.

The following information is collected as a part of the event:

1. The clustered status of the instance (if it's actually clustered or not)
2. The number of nodes present in the cluster at the time
3. The maximum number of nodes allowed by your license
4. The maximum number of users allowed by your license

For more information about what analytics information is collected (as well as how to disable analytics collection), please see the Confluence Data Collection