[Docs] `usage/subscription/model-pricing` is very out of date.

### 📝 Reference

https://github.com/lobehub/lobe-chat/tree/main/docs/usage/subscription/model-pricing.mdx

### 🐛 Feedback

This page is very out of date. Many models listed there aren't even available in the UI right now. 
And many models in the UI are missing from this page...