Our next goal is to build the functionalities so that a user can register a new account and sign in to the account like the following:
We need to add a right bar button to enable sign-in.
If the user clicks on the bar button, the app should show an alert to give the user an option to put their email and password. It should also give them the option to register a new account.
If the user clicks the 'Sign in' button, it should sign the user in using Firebase authentication.
If the user clicks on the 'Register' button, it should open the registration screen to allow the user to create a new account.
