Load notebook instance directly from GitHub

[james-jory]

Given that the number of workshops and supporting screenshots and images has increased, we are running into the archive max size limit when initializing the workshop's CodeCommit repo. By switching from using a CodeCommit repo to directly cloning from a GitHub repo for the workshops, we avoid the limit issue. Besides, I think the current approach was being used before the project was open-sourced and publicly available for cloning into a SM instance (which is no longer the case).

The DefaultCodeRepository value on the NotebookInstance should default to the upstream repo (https://github.com/aws-samples/retail-demo-store.git) but support being overridden using the GitHubUser template parameter so developers can test changes from their fork. So something like:

DefaultCodeRepository: !Sub 'https://github.com/${GitHubUser}/retail-demo-store.git'

This will require the GitHubUser parameter to have a default of aws-samples in the root template.yaml.

Be sure to remove the steps in the root stage.sh that create and upload the retaildemostore-notebooks.zip file and verify that any notebook dependencies on the generator code and products & users data files are updated to refer to their original location in the repo. May just be the Amplitude workshop that is potentially impacted.