Fix sonarqube Images tags and buttons should have an alt attribute

src/app/core/components/anis-nav.component.html

 <nav class="navbar navbar-light bg-light navbar-expand-md fixed-top border-bottom">
     <!-- Logo -->
     <a href="/" class="navbar-brand">
-        <img src="../assets/cesam_anis80.png" />
+        <img src="../assets/cesam_anis80.png" alt="CeSAM logo"/>
     </a>
 
     <!-- Right Navigation -->

src/app/search/components/result/renderer/img.component.html

-<img [src]="src">
\ No newline at end of file
+<img [src]="src" [alt]="src">
\ No newline at end of file

src/app/search/components/result/renderer/thumbnail.component.html

 <button class="btn btn-link" (click)="openModal(modal)">
-    <img [src]="src" class="img-fluid">
+    <img [src]="src" [alt]="src" class="img-fluid">
 </button>
 
 <ng-template #modal>
@@ -10,6 +10,6 @@
         </button>
     </div>
     <div class="modal-body text-center">
-        <img [src]="src" class="img-fluid">
+        <img [src]="src" [alt]="src" class="img-fluid">
     </div>
 </ng-template>
\ No newline at end of file