Add event callback prop to Auth UI component

[0xturner]

It would be handy if the Auth component received an event callback prop so that developers could trigger actions when the internal state changes.

The usage in React might look something like this:

<Auth
    ...
    onAuthEvent={(event) => {
        if (event === "sign_in") {
            foo();
        } else if (event === "sign_up") {
            bar();
        }
    }}
/>

My specific use case: When a user signs up I would like to hide the Auth component and display a custom component view in its place.

I would be happy to submit a PR for this feature but I would like to receive feedback on the feature idea before starting on the implementation.

[justin-gurtz]

I was about to create a similar discussion, I have a use case where I need to know the Auth UI view state in order to update surrounding components.

(By the way this seems similar to https://github.com/orgs/supabase/discussions/14646)