Update Optix version to 7.6

[jmahovsky-dwa]

( this one looks wrong )
https://github.anim.dreamworks.com/OpenMoonRay/openmoonray/blob/main/building/Centos7/centos7_build.md#building-moonray-on-centos-7

( also wrong )
https://github.anim.dreamworks.com/OpenMoonRay/openmoonray/blob/main/building/Rocky9/rocky9_build.md#building-moonray-on-rocky-linux-9

this looks wrong:
https://docs.openmoonray.org/getting-started/installation/building-moonray/general_build/#3.%20Optix

Jon: I think we should probably remove the build instructions from our docs site and keep the .md files in the openmoonray repo building / dir.

[jlanz]

Maybe we can just have a single page that says to look in the building/ dir of the openmoonray repo and find the instructions for your OS.
https://github.com/dreamworksanimation/openmoonray/tree/release/building