Exposing default codec from codec service (opensearch-project#18698)

* Exposing default codec from codec service

Signed-off-by: bharath-techie <bharath78910@gmail.com>

* addressing comments

Signed-off-by: bharath-techie <bharath78910@gmail.com>

---------

Signed-off-by: bharath-techie <bharath78910@gmail.com>

Author: bharath-techie

server/src/main/java/org/opensearch/index/codec/CodecService.java

@@ -93,6 +93,13 @@ public CodecService(@Nullable MapperService mapperService, IndexSettings indexSe
         this.codecs = codecs.immutableMap();
     }
 
+    /**
+     * Returns default codec
+     */
+    public final Codec defaultCodec() {
+        return codecs.get(DEFAULT_CODEC);
+    }
+
     public Codec codec(String name) {
         Codec codec = codecs.get(name);
         if (codec == null) {