Mis-labelled column in systems metadata: `panel_capacity_W_each`

[JamieTaylor-TUOS]

When downloading system metadata using either search() or get_metadata(), you have labelled the System Size field from PVOutput as system_AC_capacity_W, but I think this may actually be the DC capacity of the system, since it seems to correspond to Panels multiplied by Panel Power (or num_panels multiplied by panel_capacity_W_each using OCF notation). Also, the Inverter Power (inverter_capacity_W) is recorded separately, and is typically considered the "AC capacity" of the system. The API docs don't make this clear though so I could be wrong.

PR to follow...

[JackKelly]

Good catch! Thanks Jamie!