use spinner when loading audit metadata

src/app/dars/dars-view/dars-view.component.html

@@ -50,7 +50,7 @@
         <h2 style="color:red">error loading metadata</h2>
       </ng-container>
       <ng-container *ngSwitchCase="'Loading'">
-        <h2>loading metadata</h2>
+        <mat-spinner></mat-spinner>
       </ng-container>
       <ng-container *ngSwitchCase="'Loaded'">
         <cse-dars-metadata-table
@@ -82,7 +82,7 @@
         <h2 style="color:red">error loading metadata</h2>
       </ng-container>
       <ng-container *ngSwitchCase="'Loading'">
-        <h2>loading metadata</h2>
+        <mat-spinner></mat-spinner>
       </ng-container>
       <ng-container *ngSwitchCase="'Loaded'">
         <cse-dars-metadata-table