Modify Album API endpoint to return a count attribute instead of a full assets array (#454)

* Change API to return assets count and change web behavior accordingly

* Refactor assets.length

* Explicitly declare type of assetCount so Dart SDK understand it

* Finished refactoring on mobile

web/src/api/open-api/api.ts

@@ -90,6 +90,12 @@ export interface AdminSignupResponseDto {
  * @interface AlbumResponseDto
  */
 export interface AlbumResponseDto {
+    /**
+     * 
+     * @type {number}
+     * @memberof AlbumResponseDto
+     */
+    'assetCount': number;
     /**
      * 
      * @type {string}