Need to expose initial storage size in the UI

It is currently not possible to set the storage size at launch in the UI. The value to expose and propagate is `cm_initial_storage_size`, which is currently [set to 100G in the default config](https://github.com/galaxyproject/cloudlaunch-registry/blob/5bb42f0b91efb615de8863d25fb639009a241437/app-registry.yaml#L2181).

It may also be necessary to proportionally set the storage size. I'm not really sure where does that get set for the latest GVL (eg, here it is for [a dev version](https://github.com/galaxyproject/cloudlaunch-registry/blob/5bb42f0b91efb615de8863d25fb639009a241437/app-registry.yaml#L552)).

This issue may be related to #33.