🐛 [delete-user-data] Not all data is deleted

### [REQUIRED] Step 2: Describe your configuration

- Extension name: **delete-user-data** (`storage-resize-images`, `firestore-send-email`, etc)
- Extension version: **0.1.29**
- Configuration values (redact info where appropriate):
- Cloud Firestore paths: **empty**
- Cloud Firestore delete mode: **recursive**
- Enable auto discovery: **yes**
- Auto discovery search depth: **3**
- Auto discovery search fields (Optional): **uid,userId,creatorId,scope.owner.id**

### [REQUIRED] Step 3: Describe the problem

Hi!

It looks like the extension has the implicit assumption that every document key contains a user ID but that may not always be the case. Or the auto discovery is not being applied. For example, consider a table "session" that has `userId` as a property but uses keys like `session/`. Looking at the current documentation and implementation, it seems like it is not possible to delete document for `session`

Case 1: Cloud Firestore paths is empty -> Enable auto discovery is not being applied
Case 2: Cloud Firestore paths is set to `sessions` -> This will remove all sessions according to the current code I believe:
```js
const paths = extractUserPaths(databasePaths, uid);
const promises = paths.map(async (path) => {
try {
logs.rtdbPathDeleting(path);
await admin.database().ref(path).remove(); // <-- Deletes whole table, we don't want that
logs.rtdbPathDeleted(path);
} catch (err) {
logs.rtdbPathError(path, err);
}
});
```
Case 3: Cloud Firestore paths is set to `sessions/{UID}` -> This will not work because the UID is not part of the key.

Are my assumptions correct or is it somehow possible to delete `session` with the current version? If not, I'd say it's a bug that the auto discovery isn't applied. Or is the issue that properties like `A.B.C` are not being resolved? What happens if the key is inside an object within the document?

Thanks a lot!

#### Steps to reproduce:

See above

##### Expected result

I'd expect that the auto discovery finds the documents in Case 1 and deletes it.

##### Actual result

Documents are not being deleted.