CHANGELOG: Add entry for delaying mongo init

Author: shreyamalviya

CHANGELOG.md

@@ -14,6 +14,8 @@ Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Changed
 - The name of the "Communicate as new user" post-breach action to "Communicate
   as backdoor user". #1410
+- Initialise MongoDB collection of attack mitigations after registration or login (if required)
+  instead of on Island startup. #1495
 
 ### Removed
 - Internet access check on agent start. #1402