update Changelog.md for version: 2.12

Changelog.md

 # Changelog
 
+## [2.12] - 2024-08-22
+- Add promote P to PE workflow.
+- Add new cleanup task
+- Rework the Kentik client
+- Update documentation of services and schedules modules
+- Enhanced Infoblox: Now pings all hosts, searches for all IPs, and checks for overlapping IP trunk subscriptions in allocated networks when creating a trunk.
+
 ## [2.11] - 2024-08-19
 - (fix) Make LibreNMS retry when a request times out
 - (fix) Adjust the mechanics of the minimum amount of links when creating an IP trunk