Add release notes page for version 23.0.0

Tempest 23.0.0 has been released [1].
This commit adds a new page for 23.0.0 release notes.

[1] https://review.opendev.org/#/c/703521/

Change-Id: If9ffb5c90c427ed3e31e9b6bcb5f6aeca483d110
diff --git a/releasenotes/source/v23.0.0.rst b/releasenotes/source/v23.0.0.rst
new file mode 100644
index 0000000..7c5edf8
--- /dev/null
+++ b/releasenotes/source/v23.0.0.rst
@@ -0,0 +1,6 @@
+=====================
+v23.0.0 Release Notes
+=====================
+
+.. release-notes:: 23.0.0 Release Notes
+   :version: 23.0.0