Update Documentation for multipart and reply-from interaction

### Prerequisites

- [X] I have written a descriptive issue title
- [X] I have searched existing issues to ensure the feature has not already been requested

### 🚀 Feature Proposal

I would like to use fastify as a reverse proxy. My current reverse proxy handles multipart form data, so a requirement for my new reverse proxy would need to handle this. I am aware that fastify-reply-from and fastify-multipart plugins are not compatible. Does anyone have any advice on creating a reverse proxy with fastify that handles multipart form data?

I believe the documentation should be updated to indicate if reply-from does not support any multipart file handling or JUST is not compatible with the multipart plugin. This would help end users decide if this plugin is acceptable for the use cases that are needed.

### Motivation

Save developers time when choosing plugins

### Example

_No response_