public CoordinatorResult<Void, CoordinatorRecord> classicGroupSync(
        RequestContext context,
        SyncGroupRequestData request,
        CompletableFuture<SyncGroupResponseData> responseFuture
    ) {
        return groupMetadataManager.classicGroupSync(
            context,
            request,
            responseFuture
        );
    }
Handles a SyncGroup request.

@param context The request context.
@param request The actual SyncGroup request.

@return A Result containing the SyncGroup response and
        a list of records to update the state machine.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupCoordinatorShard.java