changelog: add entry for per-callsite rate-limited logging

Add an entry under the Unreleased section documenting the new
per-callsite rate-limited logging macros and the migration of
guest-triggered high-rate callsites.

Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>

Author: kalyazin

CHANGELOG.md

@@ -10,6 +10,12 @@ and this project adheres to
 
 ### Added
 
+- [#xxxx](https://github.com/firecracker-microvm/firecracker/pull/xxxx): Add
+  per-callsite rate limiting for guest-triggered log paths via the
+  `error_rate_limited!` macro. High-rate callsites in balloon, net, block, PCI,
+  and MMIO device paths are migrated to use rate-limited logging with a fixed
+  budget of 10 messages per 5-second window. A new `rate_limited_log_count`
+  metric tracks the total number of suppressed messages.
 - [#5323](https://github.com/firecracker-microvm/firecracker/pull/5323): Add
   support for Vsock Unix domain socket path overriding on snapshot restore. More
   information can be found in the