Given a GH repo link, clone it into the sandbox

[amanape]

Summary
Future UI will support the user to select a GH repo they would like to start with (optionally). If that is the case, the sandbox will also have to clone the repo to work with.

Motivation
New features and UI

Technical Design
The GH repo ({owner}/{repo}) could be passed to the backend via the config. This will then be used to clone the project during initialization.

Things to Consider
The user will not have direct access to this project in their file system as it will be in a Docker container. This may imply that we would want to create a separate container for each new project.

Additional Context
Blocks #3604

[shubhamofbce]

This will be a great addition.

[amanape]

Moved to #3736