[Next CET update] Output metric benefit fields, similar to metric cost fields, in the CET output

The CET outputs metric cost fields, e.g. TRCCost, PACCost, but does not output equivalent metric benefit fields. This work will add metric benefit fields, e.g. TRCBen and PACBen.

In the past, the benefit calculation/number was the same for all the CE metrics - electric benefits + gas benefits - but now each of the metrics has a different benefit calculation.