chore(changelog): add entry for log file creation

Add a change log entry for the new behaviour of creating the log and
metrics file if they don't exist.

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

CHANGELOG.md

@@ -16,6 +16,10 @@ and this project adheres to
 
 ### Changed
 
+- [#4028](https://github.com/firecracker-microvm/firecracker/pull/4028):
+  Firecracker now creates the log and metrics files if they do not exist,
+  simplifying the launch of Firecracker by removing a manual step.
+
 ### Deprecated
 
 ### Removed