Max file size caps at 1GB

*This issue was originally created by [**@TheTacomancer**](https://github.com/TheTacomancer) at .*

### Background information

- **Dendrite version or git SHA**: Dendrite 0.13.4
- **SQLite3 or Postgres?**: Postgres
- **Running in Docker?**: No
- **`go version`**: go1.21.3 linux/amd64
- **Client used (if applicable)**: Element

### Description

- **What** is the problem: The max file size caps at 1GB after attempting to change it in both the config file and a caddy json file
- **Who** is affected: All clients on the server, I am the administrator of the server
- **How** is this bug manifesting: Not sure, logs don't seem to be reporting a problem
- **When** did this first appear: 11/07/23 right after changing the config files

### Steps to reproduce

- set up dendrite server following mostly comfy.guide (for example making a dendrite user and putting the server in /opt/dendrite)
- change caddy file to increase request_body to 11811160064
- change dendrite config to be the same size

Thank you for your time