fix(accessibility): Added landmark roles and accessible carto

Related to [Accessibilité] - Lighthouse + IBM scans (#547 - closed)

src/app/admin/components/nav-bar/nav-bar.component.html

-<header>
+<div class="header">
   <h1>Administration</h1>
   <nav>
     <app-button
@@ -34,4 +34,4 @@
     />
     <app-button [variant]="'tertiary'" [label]="'Ghost'" (action)="openGhost()" />
   </nav>
-</header>
+</div>