KAFKA-7699: KIP-1146 notable change docs for 4.2.0 (#20903)

Update `Notable changes in 4.2.0` in `docs/upgrade.html` with
information about
[KIP-1146](https://cwiki.apache.org/confluence/x/9QqWF).

Reviewers: Bill Bejeck<[email protected]>

---------

Co-authored-by: Bill Bejeck <[email protected]>

Author: hermanjakobsen

docs/upgrade.html

@@ -217,6 +217,10 @@ <h5><a id="upgrade_420_notable" href="#upgrade_420_notable">Notable changes in 4
         policy. The <code>PrincipalConnectorClientConfigOverridePolicy</code> policy is now deprecated and will be removed in Kafka 5.0.0.
         For further details, please refer to <a href="https://cwiki.apache.org/confluence/x/2IkvFg">KIP-1188</a>.
     </li>
+    <li>
+        It is now possible to specify the start time for a Kafka Streams punctuation, instead of relying on the non-deterministic time when you register it.
+        For further details, please refer to <a href="https://cwiki.apache.org/confluence/x/9QqWF">KIP-1146</a>.
+    </li>
 </ul>
 
 <h4><a id="upgrade_4_1_0" href="#upgrade_4_1_0">Upgrading to 4.1.0</a></h4>