[FR] Offer additional Gotrue authentication providers for login

### Feature Description

The AppFlowy Web app currently offers login through a predefined set of login providers.

These are taken from Gotrue, which also offers other options.

While it is currently possible to use those, such as GitLab, to login to the admin console, and indirectly through it, to the Flutter desktop and mobile apps, there is currently no path towards doing so with the Web distribution.

Following on from https://github.com/AppFlowy-IO/AppFlowy-Web/issues/105#issuecomment-3319199033 https://github.com/AppFlowy-IO/AppFlowy-Web/issues/139#issuecomment-3319284627 I would like to propose to also

- Offer additional Gotrue authentication providers for login

### Use Cases

Using all AppFlowy runtime environments in self-hosted environments together with a self-hosted identity provider.

### User Impact

AppFlowy instances from self-hosted communities don't leak Personally Identifying Information (PII) / personal data to commercial platform providers, eventually in different jurisdictions.

This is relevant for running the application within the EU, where GDPR compliance and an explicit data transfer agreement are non-optional.

### Potential Implementation Ideas

The stories

- https://github.com/AppFlowy-IO/AppFlowy-Cloud/issues/621
- https://github.com/AppFlowy-IO/AppFlowy-Cloud/pull/874

have previously shown a client-side implementation for the admin frontend console.

### Additional Context

The Flutter app has a mirroring story:

- https://github.com/AppFlowy-IO/AppFlowy/issues/5534