Similar to the "Audit Log" screens on the Project Settings and Repository Settings pages, add "Audit Log" on the Administration page (https://<bitbucketserver>/admin) that will show system level audit events, such as Server, User Management, Permission events.

Also, add option to export the audit log in the Support Zip

Related Stack overflow question:

https://stackoverflow.com/questions/48622866/how-do-i-view-the-system-level-audit-log-events-via-the-bitbucket-server-ui/48624000#48624000