Use heatsource based on varying supply temperature

[tolga-akan]

Use heatsource if asset max temperature is larger than or equal to network supply temperature for the case with network supply temperature has multiple temperature options:

• Modify heat_physics_mixing so that heat_out of heat_source will be zero if network supply temperature is greater than the max temperature of the asset. Apply this to all the supply temperature options
• Create a new test. Place 2 heat source and set the cheap heat source maximum temperature lower than the network supply temperature. Define multiple temperature options to the supply temperature. Show that optimizer uses only expensive heat source and smallest supply temperature is selected.

[tolga-akan]

@KobusVanRooyen Ready to review.

Currently I created the temperature_regimes list inside the problem class by using the carrier names. This list includes the temperatures of <base_carrier_name>_. Shall we define the list of temperature regimes in esdl_parser? Do you think the current way of defining of the list is enough for the time being.