Create a service for easy data updates

[ellenhp]

This init container thing we do right now doesn't scale well to cover the planet. It's not reasonable to have one copy of each artifact per pod when the artifacts are tens or hundreds of gigabytes. My current plan is to create a longhorn RWX volume claim and share that between all of the pods. Each pod will mount the volume claim as read-only and serve data out of it. I'll have to write a new service to manage the data that's kept in the pvc and help do the following:

1. download new data when it becomes available
2. restart the deployments as necessary when they need to start serving new data
3. determine when it's safe to delete old data by examining running pods
4. actually delete the old data once it's safe

That service will need to be able to access the cluster's api (kubelet? still getting up to speed on terminology) for items 2 and 3.