Delete Derivative Files after 90 or 120 Days

[ianmilligan1]

Right now we're using about 3TB of space for storing old derivatives. This will begin to balloon and we could have lots of unused derivatives lying fallow, taking up space (and ultimately costing money on the production instance).

We should consider implanting a 90 or 120 day timeout on the derivatives.

That said, it would be nice if there was a flag we could set to keep derivatives on the system in certain situations (i.e. a few of our collections for testing purposes; if there's a particular use case; etc.).

[ruebot]

This really isn't an issue with the Compute Canada infrastructure. But, if we move some where with cost implications, then it is definitely a priority.

I'm going to mark this as on-hold for now since it is a ways down the road.

[SamFritz]

Updating to include related ticket #391 that discusses possible development and implemention of a data retention policy