add gateway bandwith to siac

MERGE REQUEST

Overview

adds a new siac gateway bandwidth command.

Example for Visual changes (ie Screenshot)

Issues Closed

This replaces !4053 (closed) which hasn't been updated in a few weeks.

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