suggestion: inform units on receiving hit

[jugglingjsons]

I was toying this idea as an alternative to handle https://github.com/lampe-games/godot-open-rts/issues/95 & make the actors more responsive to each other. I was not sold on, units auto attacking in sight range, seems a bit too offensive to me, so here is the idea for a Defend Your Friend doctrine.

To be honest I am not sure if this does anything right now, I will try to test it out soon ™️

Right now it should act as a defensive reaction, where units support each other, but could also be added to the offensive stances.

If you like it, the do adjust would be the following:

• [ ] adjust the signal for offensive stance
• [ ] don't set auxiliary target on workers
• [ ] possibly filter signals by team