docs: Add medical image migration guide from PyTorch to MindSpore

### What type of PR is this?
/kind feature

### What does this PR do / why do we need it?
This PR introduces a comprehensive migration guide for medical imaging models from PyTorch to MindSpore, addressing key technical challenges:

1. **Data Loading Adaptation**: 
   - Comparative analysis between PyTorch Dataset and MindSpore GeneratorDataset implementations
   - 3D medical image preprocessing pipeline optimization

2. **Network Structure Conversion**:
   - Compatibility solutions for 3D convolution layers and interpolation operations
   - Weight initialization verification methodology

3. **Training Process Refactoring**:
   - Automatic differentiation workflow demonstration
   - Mixed-precision training best practices

4. **Debugging Techniques**:
   - Dimension mismatch troubleshooting matrix
   - Performance comparison metrics (PyTorch vs MindSpore)

**Which issue(s) this PR fixes**:

Fixes #

**Special notes for your reviewers**:

MindSpore/docs .gitee-modal { width: 500px !important; }

搜索帮助

MindSpore/docs