New method in router to create CRUD for a Django model.

[rroblf01]

This pull request adds comprehensive documentation for the new auto-generated Model API feature in Django Ninja. The documentation explains how to quickly generate full CRUD endpoints for any Django model using a single method call, details the generated routes and schemas, and describes all available configuration options. It also covers the async variant for projects using Django's async ORM, provides a full example, and compares the auto-generated API to manual CRUD implementations. Additionally, the new documentation page is integrated into the guides navigation.

Documentation for auto-generated Model API:

• Added a new guide (guides/model-api.md) detailing how to use add_model_api and add_async_model_api to automatically generate CRUD endpoints for Django models, including descriptions of generated endpoints, schemas, parameters (fields, exclude, operations, tags, auth), and usage examples.
• Explained the difference between sync and async variants, when to use each, and highlighted that both produce identical OpenAPI schemas.
• Included a side-by-side comparison showing how the auto-generated API replaces manual CRUD endpoint definitions.

Documentation navigation update:

• Added the new "Auto-generated Model API" guide to the documentation navigation in mkdocs.yml for easy discoverability.