CollectionReference object can be used for adding documents, getting
document references, and querying for documents (using the methods
Firestore for the Firestore database (useful for performing
The collection's identifier.
A reference to the containing
DocumentReference if this is a subcollection.
If this isn't a subcollection, the reference is null.
A string representing the path of the referenced collection (relative to the root of the database).
Add a new document to this collection with the specified data, assigning it a document ID automatically.
An Object containing the data for the new document.
A Promise resolved with a
DocumentReferencepointing to the newly created document after it has been written to the backend.