MINOR: Update upgrade steps (#19132)

Using `bin/kafka-features.sh upgrade --metadata 4.0` to finalize the
upgrade is deprecated and furthermore it does not bump all the other
feature flags. Hence we should recommend to use `bin/kafka-features.sh
upgrade --release-version 4.0` in the documentation. This change was
introduced in [KIP-1022: Formatting and Updating
Features](https://cwiki.apache.org/confluence/display/KAFKA/KIP-1022%3A+Formatting+and+Updating+Features).

Reviewers: Chia-Ping Tsai <[email protected]>, Ismael Juma <[email protected]>

Author: dajac

docs/upgrade.html

@@ -37,9 +37,9 @@ <h4><a id="upgrade_4_0_0" href="#upgrade_4_0_0">Upgrading to 4.0.0 from any vers
     <li>Upgrade the brokers one at a time: shut down the broker, update the code, and restart it. Once you have done so, the
         brokers will be running the latest version and you can verify that the cluster's behavior and performance meets expectations.
     </li>
-    <li>Once the cluster's behavior and performance has been verified, bump the metadata.version by running
+    <li>Once the cluster's behavior and performance has been verified, finalize the upgrade by running
         <code>
-            bin/kafka-features.sh upgrade --metadata 4.0
+            bin/kafka-features.sh upgrade --release-version 4.0
         </code>
     </li>
     <li>Note that cluster metadata downgrade is not supported in this version since it has metadata changes.