feat(api): add LLM model configurations endpoint and schemas

- Introduce new API route `/access` for managing LLM model configurations
- Add LLMModelConfig model to database models
- Include comprehensive schemas for LLM model config CRUD operations
- Register new router with tags for LLM Model Configurations

gns3server/db/models/__init__.py

@@ -23,6 +23,7 @@ from .privileges import Privilege
 from .computes import Compute
 from .images import Image
 from .pools import Resource, ResourcePool
+from .llm_model_configs import LLMModelConfig
 from .templates import (
     Template,
     CloudTemplate,