Add libosqp

[traversaro]

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PR to add the C library for https://github.com/oxfordcontrol/osqp , as discussed in conda-forge/osqp-feedstock#25 . It is probably not ready as osqp uses a qdldl git submodule, that is not present in the release archive, see conda-forge/conda-forge.github.io#619 for a related discussion.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/libosqp) and found it was in an excellent condition.

[traversaro]

The port should be now ready to be merged. Regarding vendored packages, at the moment osqp vendors qdldl, however de-vendoring it is not trivial ( see osqp/osqp#85) so for now it is included with its license, and once the libosqp-feedstock is in place I will work to remove it, before packaging other package that depend on qdldl as well (see conda-forge/scs-feedstock#18).

[traversaro]

The PR is ready for review.
fyi @conda-forge/help-c-cpp (because the library is written in C) @wolfv (because the library is quite used in robotics, see for example https://github.com/ros-industrial-consortium/trajopt_ros and is also vendored in ROS2 : ros/rosdistro#27246) @conda-forge/osqp (for the discussion in conda-forge/osqp-feedstock#25)

@h-vetinari was added among the mantainers as he requested it in conda-forge/osqp-feedstock#25 (comment) .