DownloadByRoot timeout

MERGE REQUEST

Overview

This MR adds a configurable timeout to the Skynet download routes. Note that this timeout is a TTFB timeout, and does not cover the entire download.

It achieves the timeout by adding a timeout to the DownloadByRoot project.
This way, a user can timebox the amount of time a node takes to find a host that has the required Skylink.

It imposes a default timeout of 30s, which is documented in the API documentation. It also adds a response header that indicates the request timed out, alongside the timeout value.

Example for Visual changes (ie Screenshot)

N/A

Issues Closed

N/A

Checklist

Review and complete the checklist to ensure that the MR is complete before assigned to an approver.

• All new methods, or updating methods have clear docstrings
• Testing added or updated for new methods
• Any new packages are added to Makefile and .gitlab-ci.yml
• API documentation updated for API updates
• Module README.md updated for changes to work flow
• Issue added to Sia-UI repo for new supporting features
• Changelog updated