Feature: implement github OAuth with a auth screen

Description:

To enhance user authentication and access to GitHub features, we need to implement a GitHub login and sign-up process with a dedicated authentication screen. This issue focuses on setting up the initial authentication flow and also making of Authentication screen design as per this figma file

Tips for the issue:

• Implement logic to check if a user is already authenticated when launching the app.
• Test the authentication flow thoroughly to ensure that users can successfully log in and sign up using their GitHub accounts.
• Use Appwrite oauth

To do:

• Ask us to assign the issue
• Once the issue is assigned, you can start working on it
• Create a PR

Resource:

• Material 3 Design
• Flutter UI docs
• Refer dev.to/OAuth/appwrite

Notes:

The task is assigned to contributors on a first-come, first-serve basis, and the contributor has to report progress every 3 days to ensure active development on the tasks.