Merge "Add ussuri prelude to release notes"

releasenotes/notes/ussuri-prelude-e7f5a1535421f9eb.yaml

+---
+prelude: |
+  The Kolla Ansible ``10.0.0`` release is the first release in the Ussuri
+  cycle. Notable changes include:
+
+  * all playbooks and scripts now use Python 3 and support for Python 2 has
+    been dropped
+  * CentOS 8 is now supported as a host operating system and container image,
+    and support for CentOS 7 has been dropped
+  * Ceph deployment support has been dropped
+  * configuration of external Ceph integration has been streamlined
+  * initial support for TLS encryption of backend API services, providing
+    end-to-end encryption of API traffic for Barbican, Cinder, Glance, Heat,
+    Horizon, Keystone, Nova and Placement
+  * support for deployment of Open Virtual Network (OVN) and integration of it
+    with Neutron