docs: Add troubleshooting guide for embedding models (fixes #9064) (#9065)

docs: Add troubleshooting guide for embedding models (#9064)

- Add section on using gallery models for embeddings
- Document common issues with embedding model configuration
- Add troubleshooting guide for Qwen3 embedding models
- Include correct configuration examples for Qwen3-Embedding-4B
- Document context size limits and dimension parameters
- Add table of Qwen3 embedding model specifications

Fixes #9064

Signed-off-by: localai-bot <localai-bot@localai.io>
Co-authored-by: localai-bot <localai-bot@localai.io>