Add CHANGELOG for GCP image features

Published images now automatically run with UEFI boot mode and have opt-in
support for GVNIC.

CHANGELOG.md

@@ -18,6 +18,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - kola tests `cl.cgroupv1` and `kubeadm.*.*.cgroupv1.base` that test functionality with cgroupv1 ([#298](https://github.com/flatcar-linux/mantle/pull/298))
 - Added private network support to qemu-unpriv platform ([#307](https://github.com/flatcar-linux/mantle/pull/307))
 - Ignition v3 support and tests ([#301](https://github.com/flatcar-linux/mantle/pull/301), [#311](https://github.com/flatcar-linux/mantle/pull/311))
+- GCP: support testing with GVNIC (TODO)
 
 ### Changed
 - removed `packet` occurrences in favor of `equinixmetal` ([#277](https://github.com/flatcar-linux/mantle/pull/277))
@@ -26,6 +27,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Bumped cilium tested version to 1.11.0 ([291](https://github.com/flatcar-linux/mantle/pull/291))
 - Bumped `etcd` and `cobra` dependencies ([#293](https://github.com/flatcar-linux/mantle/pull/293))
 - Bumped Kubernetes binaries and CNI versions ([#297](https://github.com/flatcar-linux/mantle/pull/297))
+- GCP images are now published/tested with UEFI boot mode (TODO)
 
 ### Removed
 - Remove `--repo-branch` option from cork ([#283](https://github.com/flatcar-linux/mantle/pull/283))