Make Apple provider Secret Key optional for native-only Sign in with Apple

[fittar]

When using native iOS Sign in with Apple (via React Native Expo), the Secret Key is not used. The OS handles authentication and provides an id_token directly to Supabase. The Secret Key is only needed for web-based OAuth flows.
However, the Apple provider settings page in the Supabase Dashboard requires a Secret Key to save any changes. This means that if you need to add a new bundle ID to the Client IDs field (e.g. when adding a new white-label app), you cannot save without also providing a Secret Key, even if you don't need one.

Expected behavior:
The Secret Key field should be optional, or the UI should clearly indicate it's only required for web-based OAuth. Developers using native-only Apple Sign In should be able to update Client IDs without being blocked.

Context:
We run multiple white-label apps (each with their own bundle ID) using native iOS Sign in with Apple. When adding a new app's bundle ID to the Client IDs list, we were blocked from saving because the Secret Key field was empty. We had to generate a secret we don't actually need, just to unlock the save button.

[anatoly-os]

Confirm for pure native iOS application written in SwiftUI. Secret key is still required, but docs states "If you're building a native app only, you do not need to configure the OAuth settings."