Normalize whitespace in source files

Ensure that no source files have trailing whitespace at end of lines and ensure that all files end with a single trailing newline.

This also adds Github Actions to enforce whitespace conventions.

src-ui/src/app/components/dashboard/widgets/statistics-widget/statistics-widget.component.ts

@@ -23,7 +23,7 @@ export class StatisticsWidgetComponent implements OnInit, OnDestroy {
   statistics: Statistics = {}
 
   subscription: Subscription
-  
+
   private getStatistics(): Observable<Statistics> {
     return this.http.get(`${environment.apiBaseUrl}statistics/`)
   }

src-ui/src/app/components/dashboard/widgets/welcome-widget/welcome-widget.component.html

@@ -13,4 +13,4 @@
     <p i18n>Consult the documentation on how to use these features. The section on basic usage also has some information on how to use paperless in general.</p>
   </ng-container>
 
-</app-widget-frame>
+</app-widget-frame>

src-ui/src/app/components/dashboard/widgets/widget-frame/widget-frame.component.html

@@ -4,9 +4,9 @@
       <h5 class="card-title mb-0">{{title}}</h5>
       <ng-content select ="[header-buttons]"></ng-content>
     </div>
-    
+
   </div>
   <div class="card-body text-dark">
     <ng-content select ="[content]"></ng-content>
   </div>
-</div>
+</div>