[FR] Can we add `shallow` support to `Query.get` like `Reference.get`...?

**Is your feature request related to a problem? Please describe.**

The addition of the `shallow` parameter when retrieving data was requested in #61 and accepted in #109, but this only added the `shallow` param to `Reference.get`. I have a `Query` (`order_by_child`) that I would like to `shallow`, but `Query.get` doesn't support the param.

**Describe the solution you'd like**

I don't see any limitation to having both the `orderByChild` and `shallow` parameters in [the docs for RTDB via Rest](https://firebase.google.com/docs/database/rest/retrieve-data), but admittedly I haven't tried it yet. If there are none, can we add `shallow` to `Query.get`, too?

**Describe alternatives you've considered**

None exist, as far as I know, if I need to select a subset of paths filtered by criteria but only want the keys of those refs. Open to suggestion otherwise...

**Additional context**

_Expected_

```python
>>> just_ids_please = (firebase_admin.db
... .reference("/path/to/resource")
... .order_by_child("some/child")
... .equal_to("some_value")
...).get(shallow=True)
...
>>>
```
_Actual_

```python
>>> just_ids_please = (firebase_admin.db
... .reference("/path/to/resource")
... .order_by_child("some/child")
... .equal_to("some_value")
...).get(shallow=True)
...
TypeError: get() got an unexpected keyword argument 'shallow'
```

Start by comparing the Query.get and Reference.get entry points against the Firebase Realtime Database REST documentation linked in the issue. Confirm whether shallow can be combined with order_by_child and equal_to, then make Query.get accept the parameter and verify that the shown filtered query returns only reference keys.

Written by the indexing model from the issue text.