chore: Add additional path to auth-v1-open-callback

[barrownicholas]

What kind of change does this PR introduce?

• bug fix for: signInWithOAuth custom provider incorrect redirect_uri auth#2477
• prefer over: fix: Update redirect URL path for OAuth callback (Issue #2477) auth#2478 (see signInWithOAuth custom provider incorrect redirect_uri auth#2477 (comment))

What is the current behavior?

In the new custom OIDC/OAuth provider, it hard-codes the redirect URI to {{KONG-GATEWAY}} /callback. Since Auth/GoTrue can be self-hosted, and not necessarily behind Kong, at /auth/v1, it seems like the callback cannot be modified in Auth/GoTrue (instead, in Kong, (see supabase/auth#2477 (comment))).

What is the new behavior?

The new behavior properly proxies /callback and /auth/v1/callback to GoTrue.

Additional context

See the issue linked above (supabase/auth#2477)

Basically, the below line of code cannot change:

https://github.com/supabase/auth/blob/2d8f2b6168cfc753f55c7bd157bfda6ef05af007/internal/api/external.go#L682

Instead, Kong needs to properly proxy /callback in the same way that it ports /auth/v1/callback

[barrownicholas]

@avallete @sweatybridge could you check this out when you have a second? Thank you!!