chore(CHANGELOG.unreleased): contains unreleased changes

Inspired by [Prettier](https://github.com/prettier/prettier/blob/master/CHANGELOG.unreleased.md).

Changes should go there instead of CHANGELOG, they will be moved during the release process.

This change should prevent the issue where old updated PRs added changes at incorrect positions in the CHANGELOG.

CHANGELOG.unreleased.md

@@ -0,0 +1,12 @@
+> This file contains all changes that have not been released yet.
+
+### Enhancements
+
+### Bug fixes
+
+- [Host] Show the host's memory usage instead of the sum of the VMs' memory usage (PR [#3924](https://github.com/vatesfr/xen-orchestra/pull/3924))
+
+### Released packages
+
+- xo-server v5.35.0
+- xo-web v5.35.0