fix: handle case when Elasticsearch index does not exist in alerts fetching

Author: mjabascal10

backend/src/main/java/com/park/utmstack/service/threat_management/AdversaryAlertsService.java

@@ -27,6 +27,11 @@ public class AdversaryAlertsService {
     private final ElasticsearchService elasticsearchService;
 
     public List<AdversaryAlertsResponseDto> fetchAdversaryAlerts(List<FilterType> filters){
+
+        if(!elasticsearchService.indexExist(V11_ALERTS_INDEX_PATTERN)) {
+            return Collections.emptyList();
+        }
+
         SearchRequest request = SearchRequest.of(s -> s
                 .index(V11_ALERTS_INDEX_PATTERN)
                 .query(SearchUtil.toQuery(filters))

backend/src/main/java/com/park/utmstack/web/rest/threat_management/AdversaryAlertsResource.java

@@ -24,6 +24,7 @@ public class AdversaryAlertsResource {
 
     @PostMapping("/alerts")
     public ResponseEntity<List<AdversaryAlertsResponseDto>> search(@RequestBody(required = false) List<FilterType> filters) {
+
             List<AdversaryAlertsResponseDto> responseDto = adversaryAlertsService.fetchAdversaryAlerts(filters);
 
             if (responseDto.isEmpty())