Add version 7.4. (#43930)

Relates #43927.

Author: jpountz

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

@@ -54,6 +54,7 @@ public class Version implements Comparable<Version>, ToXContentFragment {
     public static final Version V_7_2_0 = new Version(7020099, org.apache.lucene.util.Version.LUCENE_8_0_0);
     public static final Version V_7_2_1 = new Version(7020199, org.apache.lucene.util.Version.LUCENE_8_0_0);
     public static final Version V_7_3_0 = new Version(7030099, org.apache.lucene.util.Version.LUCENE_8_1_0);
+    public static final Version V_7_4_0 = new Version(7040099, org.apache.lucene.util.Version.LUCENE_8_1_0);
     public static final Version V_8_0_0 = new Version(8000099, org.apache.lucene.util.Version.LUCENE_8_1_0);
     public static final Version CURRENT = V_8_0_0;