feat: support `max_upload_dir_size` config

[Narayanbhat166]

Description

This Pull Request adds a feature to limit the uploads if the ./uploads dir is full. The size of ./uploads dir can be set by the config key max_upload_dir_size under the server config.

[server]
max_upload_dir_size = "100G"

Motivation and Context

This is required to restrict the number / size of uploads that can be made to the server when hosted publicly. This fixes #282

How Has This Been Tested?

Changelog Entry

• Add a check for the max size of uploads directory

Types of Changes

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [x] I have formatted the code with rustfmt.
• [x] I checked the lints with clippy.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.