Add WLS license to CI

[simonbowly]

This is needed already for the cardinality-constrained regression doctests (quadratic model with >200 variables), and will also be needed for several OPF mod unittests.

To do:

• Enable full WLS license for doc tests. Change doctest execution to push/main and pull_request_target/labelled
• Mark tests to skip if the pip license is detected
• Add an action to run unittest with WLS. Execute on push/main and pull_request_target/labelled

[simonbowly]

For the release job which runs many platforms and python versions in parallel, the license needs a baseline limit of at least 12

[rluce]

Somwhere in the docs we state that all examples are runnable with the vendored pip license. Can we integrate WLS in the CI and still verify that property?

[simonbowly]

Good point, then we should not apply the WLS license to the doctests, only to a secondary run of the unittests.

I can adjust the cardinality-constrained regression mod to respect that limit in doctests, not sure if the OPF mod examples can do the same.

[simonbowly]

FWIW there is a skipif directive in sphinx-doctest which would allow us to do a run of the doctests with and without a full license. But maybe we should wait on that to enforce small examples as long as we can.