Update upstream opensearch version (#89)

According to latest branching strategy,
main should track 3.0.0-snapshot, next major version.

Signed-off-by: Vijayan Balasubramanian <balasvij@amazon.com>

build.gradle

@@ -45,7 +45,7 @@ validateNebulaPom.enabled = false
 
 buildscript {
     ext {
-        opensearch_version = System.getProperty("opensearch.version", "2.2.0-SNAPSHOT")
+        opensearch_version = System.getProperty("opensearch.version", "3.0.0-SNAPSHOT")
         version_qualifier = System.getProperty("build.version_qualifier", "")
         opensearch_group = "org.opensearch"
     }