bump version to 2.2.0 (opensearch-project#215)

Signed-off-by: Rishabh Maurya <rishabhmaurya05@gmail.com>

Co-authored-by: Maurya <rishma@88665a52f373.ant.amazon.com>

build.gradle

@@ -7,7 +7,7 @@ import org.opensearch.gradle.test.RestIntegTestTask
 
 buildscript {
     ext {
-        opensearch_version = System.getProperty("opensearch.version", "2.1.0-SNAPSHOT")
+        opensearch_version = System.getProperty("opensearch.version", "2.2.0-SNAPSHOT")
         isSnapshot = "true" == System.getProperty("build.snapshot", "true")
         buildVersionQualifier = System.getProperty("build.version_qualifier", "")
     }