### What problem does this PR solve?
feat: Added LLM factory initialization functionality and knowledge base
related API interfaces
refactor(dao): Refactored the TenantLLMDAO query method
feat(handler): Implemented knowledge base related API endpoints
feat(service): Added LLM API key setting functionality
feat(model): Extended the knowledge base model definition
feat(config): Added default user LLM configuration
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
