The `workspace-full` takes a long time to `docker pull` in a first run of `gp rebuild`

[loujaybee]

When running gp rebuild for the first time, the docker pull takes quite a long time, as it's typically using workspace-full as the default image, which takes a long time to pull. We should find ways to encourage users to build smaller, more slimline workspace images, or re-using our existing workspace-images.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.