fix: Add comment property to DriveFile (#46)

* Add comment property to DriveFile

Some components of Misskey like the image viewer use this property, but it hasn't been defined in the type definition itself.

* Make DriveFile.comment nullable

There's a few places in the client code that checks for a null comment,
suggesting this field may be set to null.

src/entities.ts

@@ -117,6 +117,7 @@ export type DriveFile = {
 	size: number;
 	md5: string;
 	blurhash: string;
+	comment: string | null;
 	properties: Record<string, any>;
 };