[Feature Request] Make more settings available to Firestore

[jtzell]

The current Firestore instance only support the following settings:
1. ProjectId
2. keyFilename
3. timestampsInSnapshots

Effort should be made to make the following settings available:
1. host
2. ssl
3. maxIdleChannels
4. ignoreUndefinedProperties

All of which are every handy for code testing and debugging in Firebase Emulators environment.

Reference to JS API: https://googleapis.dev/nodejs/firestore/latest/Firestore.html