Fix configuration and compilation against assimp 5

[traversaro]

assimp 5 does not export the same CMake variables as assimp 4, so it is necessary to change the CMake commands to link with assimp depending on the assimp version used.

For reference, this are the CMake config for assimp 5 and 4:

• https://github.com/assimp/assimp/blob/v5.0.1/assimpTargets.cmake.in
• https://github.com/assimp/assimp/blob/v4.1.0/assimp-config.cmake.in

This PR also:

• Fixes the cmake package name of assimp, that is not ASSIMP , but always assimp .
• Enables testing against assimp in macOS and Windows in GitHub Actions
• Release v1.0.3 that contains the hot fix of compatibility with Assimp 5.

Fix #601

[traversaro]

Unfortunately this fixes the compilation just with the vcpkg-generated assimp, so it only fixes #601 .