doc(changelog): add entry for EVENT_IDX support in vsock device

Add a CHANGELOG.md entry documenting the new notification suppression
support in the virtio-vsock device via the EVENT_IDX virtio feature.

Signed-off-by: Riccardo Mancini <mancio@amazon.com>

Author: Manciukic

CHANGELOG.md

@@ -33,6 +33,9 @@ and this project adheres to
 - [#5789](https://github.com/firecracker-microvm/firecracker/pull/5789): Add
   rate-limiter support to virtio-pmem device to allow control over I/O bandwidth
   generated by the FLUSH requests from the guest.
+- [#5872](https://github.com/firecracker-microvm/firecracker/pull/5872): Add
+  notification suppression support in the virtio-vsock device via the EVENT_IDX
+  virtio feature to reduce device overhead.
 
 ### Changed