[auth-ui] expose a way to provide a callback when the authentication suceeds

[ranile]

There is no way to redirect a user to a specific page after authenticating with auth-ui. There are hacky workarounds such as the one described at https://github.com/orgs/supabase/discussions/2842#discussioncomment-5602365 but they're not ideal. Without using auth-ui, the simple solution would be

await supabase.signIn()
await goto("/my/route")

but that is not possible as the signIn call is abstracted away and there is no way to run code after sign in at the moment