🚀 Enhancement: Chunk size change in .env

### 🔖 Enhancement description Adding a line within the .env to allow users to change the chunk size of large file uploads. ### 🎤 Pitch I am using appwrite to manage large files for my drone service company. When uploading large files to appwrite it becomes painfully slow. This is because of the small chunks. So allowing users to change this should fix this issue. ### 👀 Have you spent some time to check if this issue has been raised before? - [X] I checked and didn't find similar issue ### 🏢 Have you read the Code of Conduct? - [X] I have read the [Code of Conduct](https://github.com/appwrite/.github/blob/main/CODE_OF_CONDUCT.md)