Set up initial config for phone verification

[tratng02]

User Story: Verify user phone number upon registering #4

Walkthrough:

1. User submit phone number to obtain code
2. Notify user when code has been sent
3. User enters code and submit

Change(s):

• Configure phone number verification with Firebase Authentication

Related package(s): https://firebase.flutter.dev/docs/auth/phone/

Future changelog/improvement:

• Split widgets
• Configure the app with Firebase admin account instead of developer's personal account
• Implement regex to validate phone number
• Save user phone number to existing database
• Fix issue related to forceResendingToken

[tratng02]

@chungquantin To test out this service, please refer to the test inputs that I've sent to our group chat.

[chungquantin]

@tratng02 Okay thank you, I will pin the issue to make sure we won't forget! 👌