OZG-5977 add multi option to file upload button

Sub Task: OZG-7574

alfa-client/libs/design-system/src/lib/form/file-upload-button/file-upload-button.component.html

@@ -31,6 +31,7 @@
   [accept]="accept"
   (click)="resetInput()"
   [disabled]="isLoading"
+  [multiple]="multi"
   [attr.data-test-id]="(id | convertForDataTest) + '-file-upload-input'"
 />
 <label

alfa-client/libs/design-system/src/lib/form/file-upload-button/file-upload-button.component.spec.ts

@@ -25,6 +25,7 @@ import { TechSharedModule } from '@alfa-client/tech-shared';
 import { getElementFromFixture } from '@alfa-client/test-utils';
 import { ComponentFixture, TestBed } from '@angular/core/testing';
 import { faker } from '@faker-js/faker';
+import { expect } from '@jest/globals';
 import { getDataTestIdOf } from 'libs/tech-shared/test/data-test';
 import { FileUploadButtonComponent } from './file-upload-button.component';
 
@@ -61,4 +62,15 @@ describe('FileUploadButtonComponent', () => {
       expect(component.resetInput).toHaveBeenCalled();
     });
   });
+
+  describe('template', () => {
+    it('should have inputs', () => {
+      component.multi = true;
+      fixture.detectChanges();
+
+      const inputElement: HTMLInputElement = getElementFromFixture(fixture, inputTestClass);
+
+      expect(inputElement.multiple).toEqual(component.multi);
+    });
+  });
 });

alfa-client/libs/design-system/src/lib/form/file-upload-button/file-upload-button.component.ts

@@ -36,6 +36,7 @@ export class FileUploadButtonComponent {
   @Input({ required: true }) id!: string;
   @Input() isLoading: boolean = false;
   @Input() accept: string = '*/*';
+  @Input() multi: boolean = false;
 
   @ViewChild('inputElement') inputElement: ElementRef = new ElementRef({});