Added LightOn Shader Properties to Traffic Light

[szylis]

This feature allows more customisation of the traffic light shaders. For example, in the case of traffic lights constructed in such a way, that there is a single bulb for red and green. And, to create a digital twin of such a construction in AWSIM, a custom shader has to be designed.

The changes include:

• introduceing the new shader parameter in the TrafficLight.cs script: "_LightOn"
• setting the value of this parameter when the light bulb state changes,

This allows to move the critical implementation of the light behaviour to be moved to the shader instead of implementing it in TrafficLight.cs.

[mackierx111]

I think adding a flag for shader is a good idea.. However, in the future We may move the AWSIM project from HDRP to URP to improve performance. If we move to URP, we may have to re-implement the shader as well, is that a problem?

see also #261

[mackierx111]

No problem for now, so I'll merge it.

[szylis]

You are right, when we switch to URP, the shader have to be re-implemented. However, I believe this should not be a big problem.