changelog: add item to fixed list
Added item to CHANGELOG fixed list regarding the GET /vm/config snapshot
bug.
### Fixed
+- GET `/vm/config` was returning a default config object after restoring from a
+ snapshot. It now correctly returns the config of the original microVM, except
+ for boot_config and the cpu_template and smt fields of the machine config,
+ which are currently lost.
- Fixed incorrect propagation of init parameters in kernel commandline.
Related to:
[#2709](https://github.com/firecracker-microvm/firecracker/issues/2709).
