`showOptionalFields` now defaults to `false`

The default value of appearance.layout.showOptionalFields (now appearance.options.showOptionalFields) has changed from true to false. Optional fields are now hidden by default during sign up.

To restore the previous behavior, explicitly set the option:

<ClerkProvider
  appearance={{
    options: {
      showOptionalFields: true,
    },
  }}
>
</ClerkProvider>