Allocations: expand to handle a multi-tiered allocation model

[dsajdak]

Sometimes we might need allocations for a resource to overlap each other or might need a way to tier an allocation. For example, a PI requests an allocation for storage and purchases X TB at an annual rate. Then 6 months down the road purchases Y TB for another year. We would either need 2 allocations for the same storage that get added together or we'd need a way to assign an attribute (amount of storage) to an expiration date. We can currently have 2 allocations for a resource on the same project now, but there's no mechanism to add the amount of storage attributes together to get one quota. This could also be used for compute time on cluster resources.

[dsajdak]

This is mainly addressed with allocation change requests. I don't think any other changes are possible in the near future so I'm closing this issue.