KAFKA-18422 add link of KIP-1124 to "rolling upgrade" section (#19097)

Add client upgrade documentation, for more information, please refer to https://cwiki.apache.org/confluence/x/y4kgF

Reviewers: TengYao Chi <[email protected]>, Chia-Ping Tsai <[email protected]>

docs/upgrade.html

@@ -36,6 +36,9 @@ <h4><a id="upgrade_4_0_0" href="#upgrade_4_0_0">Upgrading to 4.0.0 from any vers
         Every <a href="https://github.com/apache/kafka/blob/trunk/server-common/src/main/java/org/apache/kafka/server/common/MetadataVersion.java">MetadataVersion</a>
         has a boolean parameter that indicates if there are metadata changes (i.e. <code>IBP_4_0_IV1(23, "4.0", "IV1", true)</code> means this version has metadata changes).
         Given your current and target versions, a downgrade is only possible if there are no metadata changes in the versions between.</li>
+    <li>For the Kafka client upgrade path, note that many deprecated APIs were removed in Kafka 4.0. Additionally, upgrading directly to 4.x from certain versions is not feasible.
+        For more information, please refer to <a href="https://cwiki.apache.org/confluence/x/y4kgF">KIP-1124</a>.
+    </li>
 </ol>
 
     <h5><a id="upgrade_400_notable" href="#upgrade_400_notable">Notable changes in 4.0.0</a></h5>