feat(commands): option to return data snapshots

[prescottprue]

Option to return snapshot object when calling callRtdb or callFirestore:

cy.callRtdb('get', 'some/data')
  .then((dataSnapshot) => {
    // dataSnapshot.key
   // dataSnapshot.val()
   // dataSnapshot.ref
  })

cy.callFirestore('get', 'some/data')
  .then((dataSnapshot) => {
    // dataSnapshot.id
   // dataSnapshot.data()
   // dataSnapshot.metadata
  })