Adding timestamp to search events

src/main/java/org/opensearch/ubl/backends/OpenSearchBackend.java

@@ -110,6 +110,7 @@ public void persistQuery(final String storeName, final QueryRequest queryRequest
 
         // What will be indexed - adheres to the queries-mapping.json
         final Map<String, Object> source = new HashMap<>();
+        source.put("timestamp", queryRequest.getTimestamp());
         source.put("queryId", queryRequest.getQueryId());
         source.put("query", queryRequest.getQuery());
         source.put("queryResponseId", queryResponse.getQueryResponseId());

src/main/java/org/opensearch/ubl/model/QueryRequest.java

@@ -10,14 +10,20 @@
 
 public class QueryRequest {
 
+    private final long timestamp;
     private final String queryId;
     private final String query;
 
     public QueryRequest(final String queryId, final String query) {
+        this.timestamp = System.currentTimeMillis();
         this.queryId = queryId;
         this.query = query;
     }
 
+    public long getTimestamp() {
+        return timestamp;
+    }
+
     public String getQueryId() {
         return queryId;
     }

src/main/resources/org/opensearch/ubl/backends/queries-mapping.json

@@ -1,6 +1,9 @@
 {
   "dynamic": false,
   "properties": {
+    "timestamp": {
+      "type": "date"
+    },
     "queryId": {
       "type": "keyword"
     },