Add/modify combiner to not need transport component

[elenya-grant]

This came up in PR #543.
Some additional combiners were added to technology_interconnections so that those combiners could be used as the commodity_stream for a finance subgroup. In the example below, the fin_combiner is used as the commodity stream in a finance subgroup but there are no downstream components of the fin_combiner (Example 23)

["solar","fin_combiner","electricity","cable"],
["natural_gas_plant","fin_combiner","electricity","cable"],

For combiners that are only included so that they can be used as the commodity stream, these combiners don't necessarily need a transport component. In the above example, this would look like:

["solar","fin_combiner","electricity"],
["natural_gas_plant","fin_combiner","electricity"],

Currently, to do this, I think the following would need to be done:

["solar","fin_combiner",["electricity_out","electricity_in1"]],
["natural_gas_plant","fin_combiner",["electricity_out","electricity_in2"]],
["solar","fin_combiner",["rated_electricity_production","rated_electricity_production1"]],
["natural_gas_plant","fin_combiner",["rated_electricity_production","rated_electricity_production2"]],
["solar","fin_combiner",["capacity_factor","electricity_capacity_factor1"]],
["natural_gas_plant","fin_combiner",["capacity_factor","electricity_capacity_factor2"]],

From PR #543:

Maybe the combiner is needed physically/ My hang up is not wanting to delineate hardware just to calculate financial stuff if the hardware is not actually a necessary part of the system. An issue would suffice here if actually addressing it is too complicated right now.

Originally posted by @jaredthomas68 in #543 (comment)