[FEATURE REQUEST] add_individual in case it's a solar inverter

[Stefan Schultheis, OE1SCS]

Is your feature request related to a problem? Please describe.
I use individual configuration to show an additional inverter generating solar power. It looks OK as I can change the flow direction (inverted_animation), but I need to add it's power to home calculation.
I have seen the function subtract_individual in the Home Configuration.
I would need add_individual to show the power consumption of home + generated power of the inverter together.
Of course it would make sense to distinguish what Individual Device get's added to the Home Consumption (makes sense for inverters, but not for others as Car Chargers and we might see both on the same chart). Therefore it could make sense to move this configuration item from Home Configuration to each Individual Configuration and select respectively. (Same for subtract_individual?)

Describe the solution you'd like

• move subtract_individual from Home Configuration to individual's configuration
• introduce add_individual to individual's configuration

Describe alternatives you've considered
I tried to invert (calculate * -1) the power of the inverter using a Helper Entity and subtract it with the existing configuration item, but it still subtracts the negative value.

Additional context
Would make the whole solution more flexible.