[ENHANCEMENT] Include filename in search snippet

Author: chibenwa

mailbox/opensearch/src/main/java/org/apache/james/mailbox/opensearch/search/OpenSearchSearchHighlighter.java

@@ -43,11 +43,13 @@
 
 public class OpenSearchSearchHighlighter implements SearchHighlighter {
     public static final String ATTACHMENT_TEXT_CONTENT_FIELD = JsonMessageConstants.ATTACHMENTS + "." + JsonMessageConstants.Attachment.TEXT_CONTENT;
+    public static final String ATTACHMENT_FILENAME_FIELD = JsonMessageConstants.ATTACHMENTS + "." + JsonMessageConstants.Attachment.FILENAME;
     public static final List<String> SNIPPET_FIELDS = List.of(
         JsonMessageConstants.MESSAGE_ID,
         JsonMessageConstants.SUBJECT,
         JsonMessageConstants.TEXT_BODY,
-        ATTACHMENT_TEXT_CONTENT_FIELD);
+        ATTACHMENT_TEXT_CONTENT_FIELD,
+        ATTACHMENT_FILENAME_FIELD);
 
     private final OpenSearchSearcher openSearchSearcher;
     private final StoreMailboxManager storeMailboxManager;
@@ -90,6 +92,7 @@ private SearchSnippet buildSearchSnippet(Hit<ObjectNode> searchResult) {
         Optional<String> highlightedTextBody = Optional.ofNullable(highlightHit.get(JsonMessageConstants.TEXT_BODY))
             .or(() -> Optional.ofNullable(highlightHit.get(JsonMessageConstants.HTML_BODY)))
             .or(() -> Optional.ofNullable(highlightHit.get(ATTACHMENT_TEXT_CONTENT_FIELD)))
+            .or(() -> Optional.ofNullable(highlightHit.get(ATTACHMENT_FILENAME_FIELD)))
             .map(List::getFirst);
 
         return new SearchSnippet(messageId, highlightedSubject, highlightedTextBody);