Register modal loading freezes when registering with an email that already exists.

[Vailorium]

Describe the bug
When registering a user, if an email that is already in use is entered, the register modal freezes.

To Reproduce
Steps to reproduce the behavior:

1. Go to the registration page.
2. Enter an email that is already registered.
3. Fill in the other required fields.
4. Click on the Register button.
5. The register modal freezes.

Expected behavior
An error message should be displayed on the email field stating that the email is already in use. The user should be able to correct the email field and register successfully.

Additional context
This issue is causing inconvenience to the users who are unable to register successfully due to this bug. It needs to be resolved as soon as possible to provide a better user experience.

Fix
Add a handler for auth/email-already-in-use.
Should also add a default handler.