add OSQP

[djsutherland]

Split from #6076.

[conda-forge-linter]

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

I wanted to let you know that I linted all conda-recipes in your PR (recipes/osqp) and found some lint.

Here's what I've got...

For recipes/osqp:

• The "source" section was expected to be a dictionary, but got a CommentedSeq.
• The "source" section was expected to be a dictionary, but got a CommentedSeq.

[djsutherland]

cc @bstellato

[bstellato]

Thanks a lot for doing so! It would be useful to have the package in conda-forge.

[djsutherland]

@conda-forge/help-c-cpp, this is ready for review:

• Will figure out Windows on the feedstock.
• Linter error is fixed by Linter supporting multiple sources conda-smithy#792; master is happy.

[djsutherland]

Might as well ping @conda-forge/staged-recipes since apparently @conda-forge/help-c-cpp is tiny....

[scopatz]

Thanks @dougalsutherland!