feat(opensearch): added opensearch 1.1 to engineversion (#18432)

Also made an issue for this (#18431)

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Author: moritzluedtke

packages/@aws-cdk/aws-opensearchservice/lib/version.ts

@@ -62,6 +62,9 @@ export class EngineVersion {
   /** AWS OpenSearch 1.0 */
   public static readonly OPENSEARCH_1_0 = EngineVersion.openSearch('1.0');
 
+  /** AWS OpenSearch 1.1 */
+  public static readonly OPENSEARCH_1_1 = EngineVersion.openSearch('1.1');
+
   /**
    * Custom ElasticSearch version
    * @param version custom version number