feat: add user signup flow

[anhappdev]

Part of #670

A user can either sign in anonymously or with email/password.
On the sign in with email/password screen, a user can also register for a new account.

To convert from an anonymous account to a registered account with email/password:

1. Tap on the User Profile button

2. Tap on the Email icon to enter an email and password

[github-actions]

MLCommons CLA bot All contributors have signed the MLCommons CLA ✍️ ✅

[anhappdev]

I am using firebase_ui_auth which provides premade screens for user sign in and sign up flow. But this plugin does not support the Windows platform officially. I don't have experience with Windows or a Windows machine to test. So I am thinking either someone with Windows experience can jump in or maybe we can drop support for Windows (for now)?

[freedomtan]

@mohitmundhragithub to help with the Windows part

[freedomtan]

Currently there is no 3rd party authentication. We can add it later (in another PR)

[anhappdev]

I removed the Firebase SDK from the Windows platform. For now, Firebase will only be supported on iOS and Android.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[anhappdev]

@freedomtan Did you have the time to review this PR? This one currently blocks some other issues.

[freedomtan]

@anhappdev I cannot find the sign-in related menu items when I built from 84df717

[anhappdev]

@freedomtan If you build the app yourself, you need to follow this guide
https://github.com/mlcommons/mobile_app_open/blob/master/docs/environment-setup/env-setup-firebase.md
and set the vars in firebase_options.env. Else all Firebase related features will be hidden / disabled.

Or you can test the APK built by the CI, which has Firebase enabled.