Refactor/pdf creation

Moved logic from ViewAlbum controller to ImageAlbumService and made PdfDocument implement ImageAlbumDocument to abstract the document process and increase flexibility.

src/main/java/NTNU/IDATT1002/service/ImageAlbumService.java

@@ -106,9 +106,15 @@ public class ImageAlbumService {
         return createImageAlbum(title, description, user, tags, new ArrayList<>());
     }
 
-
-    public ImageAlbumDocument getDocument(Long currentAlbumId) {
-        ImageAlbum imageAlbum = getImageAlbumById(currentAlbumId)
+    /**
+     * Create and return a new document for the image album with the given id.
+     * The document is saved to the users dowloads folder.
+     *
+     * @param albumId the album id to get a document for
+     * @return the document created
+     */
+    public ImageAlbumDocument getDocument(Long albumId) {
+        ImageAlbum imageAlbum = getImageAlbumById(albumId)
                 .orElseThrow(IllegalArgumentException::new);
 
         String destinationFile = String.format("%s/downloads/%s.pdf",