select/dropdown additionalField type (more fieldTypes in general)

Github issue:

https://github.com/daveyplate/better-auth-ui/issues/182

I have a few use cases (e.g. a timezone selector) that require a select field type for an additionalField. As you can imagine, the currently supported field types don’t work well when the user should be presented with a pre-defined set of options from which to choose.

And in general, it would be really helpful if you’d consider expanding fieldType definitions to encompass a broader set of the most common form input types (e.g. select and multiselect).