Increment version to 2.4.0-SNAPSHOT (#505) (#573)

Signed-off-by: opensearch-ci-bot <opensearch-infra@amazon.com>

Signed-off-by: opensearch-ci-bot <opensearch-infra@amazon.com>
Co-authored-by: opensearch-ci-bot <opensearch-infra@amazon.com>
(cherry picked from commit 5951038)

Co-authored-by: opensearch-trigger-bot[bot] <98922864+opensearch-trigger-bot[bot]@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

build.gradle

@@ -14,7 +14,7 @@ import java.util.function.Predicate
 buildscript {
     ext {
         isSnapshot = "true" == System.getProperty("build.snapshot", "true")
-        opensearch_version = System.getProperty("opensearch.version", "2.3.0-SNAPSHOT")
+        opensearch_version = System.getProperty("opensearch.version", "2.4.0-SNAPSHOT")
         buildVersionQualifier = System.getProperty("build.version_qualifier", "")
         // 2.2.0-SNAPSHOT -> 2.2.0.0-SNAPSHOT
         version_tokens = opensearch_version.tokenize('-')