Add 3.7.3 release notes.

Author: GrahamDumpleton

project-docs/index.rst

@@ -96,6 +96,7 @@ Educates
   :maxdepth: 2
   :caption: Release Notes:
 
+  release-notes/version-3.7.3
   release-notes/version-3.7.2
   release-notes/version-3.7.1
   release-notes/version-3.7.0

project-docs/release-notes/version-3.7.3.md

@@ -0,0 +1,15 @@
+Version 3.7.3
+=============
+
+Features Changed
+----------------
+
+* The training portal has been made more resilient when allocating and
+  managing workshop sessions under load. Previously, when many sessions were
+  being requested at the same time, or when the Kubernetes REST API was slow
+  to respond or applying throttling, session allocation could fail or requests
+  could back up, sometimes surfacing as a `database is locked` error or as
+  failed or timed out session requests. Updates the training portal makes to
+  Kubernetes are now performed in a way that no longer blocks other session
+  activity while waiting on the Kubernetes API, reducing failed sessions and
+  improving reliability under high traffic.