Create the sign in flow

Google authentication using Firebase has to be implemented on the index page.

## Task
The page currently contains a text and a button. These will be updated later when their designs are ready. For now, implement the sign in flow for Google Authentication using Firebase.

**Important**
Only a select group of users should be allowed access into the portal. Implement this with `Custom Claims` Here is more on it - https://firebase.google.com/docs/auth/admin/custom-claims & https://firebase.google.com/docs/database/security/user-security

Upon successful authentication, the user should be directed to the `Home` page. Also, if the user was pre-authenticated, ie a user was already logged in, you need to forward him directly to `Home` page.