Increment version to 2.18.1 (opensearch-project#16571)

Update Version.java

Signed-off-by: Andriy Redko <andriy.redko@aiven.io>
Co-authored-by: opensearch-ci-bot <83309141+opensearch-ci-bot@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

.ci/bwcVersions

@@ -98,3 +98,4 @@ BWC_VERSION:
   - "2.17.0"
   - "2.17.1"
   - "2.17.2"
+  - "2.18.0"

buildSrc/version.properties

@@ -1,4 +1,4 @@
-opensearch        = 2.18.0
+opensearch        = 2.18.1
 lucene            = 9.12.0
 
 bundled_jdk_vendor = adoptium

libs/core/src/main/java/org/opensearch/Version.java

@@ -142,7 +142,8 @@ public class Version implements Comparable<Version>, ToXContentFragment {
     public static final Version V_2_17_1 = new Version(2170199, org.apache.lucene.util.Version.LUCENE_9_11_1);
     public static final Version V_2_17_2 = new Version(2170299, org.apache.lucene.util.Version.LUCENE_9_11_1);
     public static final Version V_2_18_0 = new Version(2180099, org.apache.lucene.util.Version.LUCENE_9_12_0);
-    public static final Version CURRENT = V_2_18_0;
+    public static final Version V_2_18_1 = new Version(2180199, org.apache.lucene.util.Version.LUCENE_9_12_0);
+    public static final Version CURRENT = V_2_18_1;
 
     public static Version fromId(int id) {
         final Version known = LegacyESVersion.idToVersion.get(id);