MDM: Add ReadRegistry instruction

MERGE REQUEST

MR Guidelines

Overview

This MR adds the second registry instruction to the MDM. The one to read an entry previously stored in the MDM.

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