Clean out uploaded resources in submission V2

[ash211]

In the first version of submission V2 the uploaded jars aren't cleaned up so will accumulate and eventually fill up the disk on the staging server pod.

We should:

1. create a default in the staging server config to delete pods N minutes after the last pod of the pod labels terminates
2. allow overriding that default in a per-upload basis with an optional field added to the uploadResources endpoint
3. consider adding a "maximum disk usage" setting that will reject resource uploads when it puts the staging server over its allotted capacity

https://github.com/apache-spark-on-k8s/spark/pull/212/files#r111496837