ONNX Runtime dependency handled by CMake without sudo on Linux

[denvoros]

This will require an update in the CI pipeline @pifopi, but now you can just let the program build itself without specifying an ONNX location, or you can have the pipeline download and install it and set ONNX_ROOT_PATH when calling cmake, e.g.:

cmake -DONNX_ROOT_PATH=/path/where/onnx/was/installed  ...

With the remainder of the options.