Add support for onnxruntime just on Linux with apt

[traversaro]

Just when ROBOTOLOGY_ENABLE_DYNAMICS_FULL_DEPS is enabled, when we are on Linux and we are not using Conda, this PR adds support for the upcoming FRAMEWORK_USE_onnxruntime option of bipedal-locomotion-framework (see ami-iit/bipedal-locomotion-framework#652).

Differently from most other dependencis handled by the robotology-superbuild, given its size and the time necessary to compile, in this case we do not compile onnxruntime from scratch, but rather we download its binaries at configuration time, and we install them. We do this just on Linux and when conda is not used.

This is just meant to be an initial test. If this binaries create problems of incompatibility with other libraries installed by apt, we will need to find another solution. Instead, for conda-provided dependencies we will try to get onnxruntime also on Windows (see conda-forge/onnxruntime-feedstock#56), and then we could add onnxruntime as any other dependency. However, let's start using this and let's see what happens.

[traversaro]

Instead, for conda-provided dependencies we will try to get onnxruntime also on Windows (see conda-forge/onnxruntime-feedstock#56), and then we could add onnxruntime as any other dependency. However, let's start using this and let's see what happens.

onnxruntime-cpp now is available in conda-forge also for Windows, so we can just add it as a dependency.