Add CreateFileTypeDto class to files.dto.ts

Introduced a new DTO class named CreateFileTypeDto in files.dto.ts for future implementations. The class currently has no properties defined, marked with a TODO comment for subsequent development.

apps/backend/src/app/files/files.dto.ts

@@ -16,3 +16,7 @@ export class CreateFilesDto {
 	@IsUUID()
 	groupId: string;
 }
+
+export class CreateFileTypeDto {
+	//TODO
+}