MINOR: Add note that streams groups are in early access (apache#19434)

Add a note to the group protocol configuration that streams groups are
in early access and should not be used in production.

Also update an outdated comment related to disabling the protocol.

Reviewers: Bruno Cadonna <[email protected]>

Author: lucasbru

core/src/main/scala/kafka/server/KafkaApis.scala

@@ -2629,16 +2629,15 @@ class KafkaApis(val requestChannel: RequestChannel,
 
   }
 
-  private def isStreamsGroupProtocolEnabled(): Boolean = {
+  private def isStreamsGroupProtocolEnabled: Boolean = {
       config.groupCoordinatorRebalanceProtocols.contains(Group.GroupType.STREAMS)
   }
 
   def handleStreamsGroupHeartbeat(request: RequestChannel.Request): CompletableFuture[Unit] = {
     val streamsGroupHeartbeatRequest = request.body[StreamsGroupHeartbeatRequest]
 
-    if (!isStreamsGroupProtocolEnabled()) {
-      // The API is not supported by the "old" group coordinator (the default). If the
-      // new one is not enabled, we fail directly here.
+    if (!isStreamsGroupProtocolEnabled) {
+      // The API is not enabled by default. If it is not enabled, we fail directly here.
       requestHelper.sendMaybeThrottle(request, streamsGroupHeartbeatRequest.getErrorResponse(Errors.UNSUPPORTED_VERSION.exception))
       CompletableFuture.completedFuture[Unit](())
     } else if (!authHelper.authorize(request.context, READ, GROUP, streamsGroupHeartbeatRequest.data.groupId)) {
@@ -2729,9 +2728,8 @@ class KafkaApis(val requestChannel: RequestChannel,
     val streamsGroupDescribeRequest = request.body[StreamsGroupDescribeRequest]
     val includeAuthorizedOperations = streamsGroupDescribeRequest.data.includeAuthorizedOperations
 
-    if (!isStreamsGroupProtocolEnabled()) {
-      // The API is not supported by the "old" group coordinator (the default). If the
-      // new one is not enabled, we fail directly here.
+    if (!isStreamsGroupProtocolEnabled) {
+      // The API is not enabled by default. If it is not enabled, we fail directly here.
       requestHelper.sendMaybeThrottle(request, request.body[StreamsGroupDescribeRequest].getErrorResponse(Errors.UNSUPPORTED_VERSION.exception))
       CompletableFuture.completedFuture[Unit](())
     } else {

group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupCoordinatorConfig.java

@@ -60,7 +60,7 @@ public class GroupCoordinatorConfig {
     ///
     public static final String GROUP_COORDINATOR_REBALANCE_PROTOCOLS_CONFIG = "group.coordinator.rebalance.protocols";
     public static final String GROUP_COORDINATOR_REBALANCE_PROTOCOLS_DOC = "The list of enabled rebalance protocols." +
-            "The " + Group.GroupType.SHARE + " rebalance protocol is in early access and therefore must not be used in production.";
+            "The " + Group.GroupType.SHARE + " and " + Group.GroupType.STREAMS + " rebalance protocols are in early access and therefore must not be used in production.";
     public static final List<String> GROUP_COORDINATOR_REBALANCE_PROTOCOLS_DEFAULT = List.of(
         Group.GroupType.CLASSIC.toString(),
         Group.GroupType.CONSUMER.toString());