Persist the SQLite database file with the grader-setup-service

[jgwerner]

The goal is to deploy the grader-setup-service to persist the SQLite database file with a volume instead of in the container's file system. This would allow us to rollout/restart the grader setup service without having to recreate all shared grader notebook deployments. It would also allow us to not have to re-create all shared grader notebook resources in case there is a failure.

The scope of this issue is focused on the grader-setup-service but could be useful for the nbgrader and JupyterHub services too when using the SQLite option during testing/dev.