Implement skynet directory upload

MERGE REQUEST

MR Guidelines

Overview

This MR enables users to upload entire directories as skyfiles. This was only available via portals or the skynet-cli until now.

There isn't much new stuff here, I basically used the UploadNewMultipartSkyfileBlocking code and added the content type detection from go-skynet.

This code will also work with large uploads because of the piped readers/writers (thanks @ChrisSchinnerl).

Example for Visual Changes

Checklist

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

• All new methods or updated 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 workflow
• [ ] Issue added to Sia-UI repo for new supporting features
• Changelog File Created

Issues Closed

Closes #4360 (closed)