Add setting to require email addresses to be unique to users

[Mosnar]

What are you trying to do?

I'm currently using the element integration to allow content authors to manage the layout of a user registration form. This works great except there isn't a way to validate that an email address isn't tied to an existing user during form validation. This results in the form submitting without errors but the integration job failing due to there already being an existing user.

What's your proposed solution?

I propose adding an option to email address fields to require the value to be unique to a Craft user.

Additional context

No response