[flutter]#1 firebase - Anonymous Login
[flutter] #2 firebase - Listen Auth State Change
[flutter] #3 firebase - Logout
[flutter] #4 firebase - Sing up With Email & Password
[flutter] #5 firebase - Sign in With Email & Password
[flutter] #6 firebase - Cloud Firestore
[flutter] #7 firebase - Firestore Stream
[flutter] #8 firebase - Firestore Stream modelling
[flutter] #9 firebase - Listing User Data
[flutter] #10 firebase - Update Firestore data