feat: Add native sign in for Kakao with OIDC

[nectarine]

I have read the CONTRIBUTING.md file.

YES

What kind of change does this PR introduce?

feature, docs update

What is the current behavior?

https://github.com/orgs/supabase/discussions/23368
Kakao provides two different keys which are REST API key, and Native app key.
Supabase accept only one key(currently REST API key), so it should accept both keys to provide seamless sign in process in native apps.

What is the new behavior?

A local dev studio doesn't show me a Provider section in Authentication > Configuration, but I added a new field for the Native app key, similar to Authorized Client IDs of Google

Also, I add the docs with native app sign in with trying my best to preserve original author's tone.

Additional context

supabase.auth also must be fixed to accept this new value EXTERNAL_KAKAO_NATIVE_APP_KEY.
(https://github.com/supabase/auth/blob/ed2b4907244281e4c54aaef74b1f4c8a8e3d97c9/internal/api/token_oidc.go#L77)
I'll make a new PR in that repository after this PR is accepted.

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