Iterator on MongoDb Adapter with GridFS fails

[tatejones]

Describe the bug
When GridFS is enabled and the iterator is called it fails.
Needs to handle the filter on filename and not the key.

How To Reproduce (best to provide workable code or tests!)

test.it.only('iterator with namespace using GridFS', async t => {
	const store = new KeyvMongo({namespace: 'key1', useGridFS: true, ...options});
	await store.set('key1:foo', 'bar');
	await store.set('key1:foo2', 'bar2');
	const iterator = store.iterator('key1');
	let entry = await iterator.next();
	// @ts-expect-error - test iterator
	t.expect(entry.value[0]).toBe('key1:foo');
});

[tatejones]

Pull requested for the fix.