Feature request: unify om_capacity parameter

[jaredthomas68]

unify om_capacity parameter across all tech including battery

As a holdover from the initial implementation of the custom financial model, and I believe from pySAM, the battery financial has a different name for the om_capacity, om_batt_capacity_cost.

Proposed solution

Ideally we would have a unified name for this, just om_capacity or om_capacity_cost regardless of technology.

Alternatives considered

Currently both om_capacity and om_batt_capacity_cost are set for battery.

Additional context

Some discussion on this from PR #355. @dguittet originally implemented the custom financial model and will likely have some insight on a good solution for HOPP.