Close [AI-40](https://linear.app/affine-design/issue/AI-40).
### What changed?
- Add anthropic provider.
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## Summary by CodeRabbit
- **New Features**
- Added support for Anthropic as a new provider option in Copilot, enabling integration with Anthropic's text generation models.
- Users can now configure Anthropic provider settings, including API key management, through the admin interface.
- **Chores**
- Updated dependencies to include the Anthropic SDK for backend operations.
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