[FEATURE] 3D Skybox in water reflections

[DESTROYGIRL]

Description

Give mappers the option to have the 3D skybox render in water reflections. This would vastly enhance the visuals for maps with large bodies of water, like rogue

Proposed Solution

Add an option to the sky_camera entity that makes the 3D skybox render in water reflections, which is turned off by default, as most maps don't require this

Alternatives Considered

Don't, because it might hurt performance for lower end systems

Additional Context

• This was implemented in CSGO as a material parameter
• I've achieved this before by changing the reflect texture in the water material, but the view was very broken.
• There are various comments about the 3d skybox and reflections in viewrender.cpp