Update release notes for 15.7 with admin ui

Make special mention of all the admin ui changes

docs/guides/admin/docs/changelog.md

@@ -6,6 +6,10 @@ Opencast 15
 
 ### Opencast 15.7
 
+- [[#6022](https://github.com/opencast/opencast/pull/6022)] -
+  Update admin interface to 2024-07-12
+- [[#6021](https://github.com/opencast/opencast/pull/6021)] -
+  Update Editor to 2024-07-12
 - [[#6004](https://github.com/opencast/opencast/pull/6004)] -
   First steps towards java 21
 - [[#6003](https://github.com/opencast/opencast/pull/6003)] -

docs/guides/admin/docs/releasenotes.md

@@ -2,7 +2,13 @@
 
 ## Opencast 15.7
 
-Opencast 15.7 release includes bug fixes and improvements.
+Opencast 15.7 release includes various smaller bug fixes and improvements.
+
+Especially the admin interface (aka new admin ui) has received a lot of attention.
+To check all the changes look at these three releases:
+  [[2024-07-12](https://github.com/opencast/opencast-admin-interface/releases/tag/2024-07-12)],
+  [[2024-07-02](https://github.com/opencast/opencast-admin-interface/releases/tag/2024-07-02)] and
+  [[2024-06-12](https://github.com/opencast/opencast-admin-interface/releases/tag/2024-06-12)].
 
 See [changelog](changelog.md#opencast-157) for a comprehensive list of changes.