Hide optix related cmake warnings

[iche033]

🦟 Bug fix

Summary

Hide optix and cuda related cmake warnings. Given that we're not actively maintaining the optix plugin, these warnings are distracting and may be misleading to users so hide them. In the future, let's consider archiving / removing the optix plugin.

Hides these warnings if cuda and optix are not available on your system:

CUDA_TOOLKIT_ROOT_DIR not found or specified
CMake Warning at /home/iche/code/gz_i_ws/install/share/cmake/gz-cmake4/cmake4/GzConfigureBuild.cmake:59 (message):
   CONFIGURATION WARNINGS:
   -- Missing dependency [OptiX]
Call Stack (most recent call first):
  CMakeLists.txt:219 (gz_configure_build)

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[scpeters]

I believe this has introduced a new cmake warning, which I was attempting to fix in gazebo-tooling/release-tools#1161

CMake Warning:
  Manually-specified variables were not used by the project:

    SKIP_optix

but that change to release-tools affects all branches. I can try adding some version logic to it actually...

[iche033]

ok thanks. The idea here is that to avoid building optix by default without having users to explicitly specify the SKIP_optix flags on ionic.