Gideon van der Merwe

**Describe the solution you'd like** I would like to make use of batch writes e.g. `firestore.batch()` and `batch().set(ref, {})` `batch().update(ref, {})` and `batch().commit()` We need this when seeding the database...

### Describe the feature you would like to see I would like to use callable functions (Firebase cloud functions). Something like this: ``` $functions = Firebase::functions(); $functions->getHttpsCallable('someCallableFunction')->call( [ 'some' =>...