docs: prepare changelog for 2021.4

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

website/docs/releases/2021.4.md

@@ -1,5 +1,5 @@
 ---
-title: Next
+title: Release 2021.4
 ---
 
 ## Headline Changes
@@ -18,6 +18,23 @@ title: Next
 
     For backwards compatibility, this is set to *all*, but new objects will default to *any*.
 
+- Expiring Events
+
+    Previously, events would stay in the database forever, and had to eventually be cleaned up manually. This version add expiry to events with a default
+    timeout of 1 Year. This also applies to existing events, and their expiry will be set during the migration.
+
+- New UI
+
+    While the UI mostly looks the same, under the hood a lot has changed. The Web UI is now a Single-page application based on rollup and lit-html. This has several consequences and new features, for example:
+
+        - You can now see a user's OAuth Access/Refresh tokens and the consents they've given
+        - You can now see a per-object changelog based on the model_create/update/delete events being created.
+        - A new API Browser is available under `https://authentink.company/api/v2beta/`
+        - Several new charts, new pages and quality-of-life improvements
+        - Credentials of objects are no longer while editing them
+
+- Deprecated Group membership has been removed.
+
 ## Upgrading
 
 This release does not introduce any new requirements.

website/sidebars.js

@@ -149,6 +149,7 @@ module.exports = {
                 "releases/2021.1",
                 "releases/2021.2",
                 "releases/2021.3",
+                "releases/2021.4",
             ],
         },
         {