Add registry subscription RPC

MERGE REQUEST

MR Guidelines

Overview

This MR adds a new RPC to the host which lets renters subscribe to changing registry values.

NOTE: This is still a draft and therefore only has basic testing. Test coverage will be improved once we are sure about the overall structure and flow.

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