Add 8.19 transport version constant to keep branches aligned (elastic#122582)

Author: ldematte

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -174,7 +174,8 @@ static TransportVersion def(int id) {
     public static final TransportVersion TIMEOUT_GET_PARAM_FOR_RESOLVE_CLUSTER = def(8_838_0_00);
     public static final TransportVersion INFERENCE_REQUEST_ADAPTIVE_RATE_LIMITING = def(8_839_0_00);
     public static final TransportVersion ML_INFERENCE_IBM_WATSONX_RERANK_ADDED = def(8_840_0_00);
-    public static final TransportVersion ELASTICSEARCH_9_0 = def(9_000_0_00);
+    public static final TransportVersion INITIAL_ELASTICSEARCH_8_19 = def(8_841_0_00);
+    public static final TransportVersion INITIAL_ELASTICSEARCH_9_0 = def(9_000_0_00);
     public static final TransportVersion REMOVE_SNAPSHOT_FAILURES_90 = def(9_000_0_01);
     public static final TransportVersion TRANSPORT_STATS_HANDLING_TIME_REQUIRED_90 = def(9_000_0_02);
     public static final TransportVersion REMOVE_DESIRED_NODE_VERSION_90 = def(9_000_0_03);

server/src/test/java/org/elasticsearch/TransportVersionTests.java

@@ -28,10 +28,12 @@
 public class TransportVersionTests extends ESTestCase {
 
     /**
-     * This test is specific for V9, to ensure that transport versions are backported correctly.
+     * This test is specific for V9, to ensure that transport versions are backported correctly. Do not forward or backport it,
+     * and do not adjust the TransportVersion to check (INITIAL_ELASTICSEARCH_9_0).
+     * If the test fails, there is something wrong with your backport PR.
      */
     public void testMaximumAllowedTransportVersion() {
-        assertThat(TransportVersions.LATEST_DEFINED.isPatchFrom(TransportVersions.ELASTICSEARCH_9_0), is(true));
+        assertThat(TransportVersions.LATEST_DEFINED.isPatchFrom(TransportVersions.INITIAL_ELASTICSEARCH_9_0), is(true));
     }
 
     public void testVersionComparison() {