open URL from SDK should use the domain got from server

[fungc-io]

After applying custom domain
The authentication flow still work without changing the endpoint,
because it uses the domain retrieve from the server.

However the open settings page method is still using the endpoint.
It will be great if it use the custom domain automatically, so it is not necessary for the user to update the app.

[joyzoursky]

Experiencing this issue when testing on version update for an exisitng app.

I think this is a should-fix bug more than enhancement issue, as it is quite often that end-user will not always keep their apps updated, then on old version they will see the invalid redirect URI error from authgear.

[louischan-oursky]

• iOS SDK Generate urls by using origin in oidc config authgear-sdk-ios#151
• Android SDK Generate urls by using origin in oidc config authgear-sdk-android#169
• React Native SDK Use origin in openid config to construct url #251
• Xamarin SDK Always use origin of authorization endpoint to build uris authgear-sdk-xamarin#76
• Flutter SDK Always use origin of authorization endpoint to open pages authgear-sdk-flutter#24

[fungc-io]

tested, all is good