Add FastAPI deployment tutorial for MONAI models (#2050)

This tutorial demonstrates how to deploy MONAI model bundles as
production-ready REST APIs using FastAPI.

Features:
- Complete FastAPI application with inference endpoints
- MONAI model bundle integration (spleen_ct_segmentation)
- Singleton pattern for efficient model loading
- Async/await for optimal performance
- Pydantic validation for type safety
- Auto-generated API documentation (Swagger/ReDoc)
- Docker deployment with multi-stage builds
- Comprehensive unit tests
- Example client code and HTTP requests
- Production-ready error handling and logging

Structure:
- app/: FastAPI application code
- tests/: Unit test suite
- docker/: Containerization configs
- examples/: Usage examples
- README.md: Complete tutorial documentation

Addresses #2048

Fixes # .

### Description
A few sentences describing the changes proposed in this pull request.

### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [ ] Avoid including large-size files in the PR.
- [ ] Clean up long text outputs from code cells in the notebook.
- [ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [ ] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

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Signed-off-by: Mohamed Salah <eng.mohamed.tawab@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>