Add stub package python-ninja

[awvwgk]

• forward dependency on ninja via python-ninja output
• add metadata for pip check
• provide possibility to use python -m ninja

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

Closes #26
Closes conda-forge/staged-recipes#19098

[conda-forge-webservices]

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 (recipe) and found it was in an excellent condition.

[henryiii]

I still believe this is not the correct fix. This won't fix other non-conda packaging ecosystems. It should be fixed upstream in the (two known) packages that misuse it, then patched there until a new version is out. If there is a python-ninja, it should be a repacking of the actual python ninja package. If someone actually does need the Python package with jobserver support, they should be able to require it. These packages do not, but just have a faulty discovery / usage of ninja only from the package.

Trying to hack around the problem is just going to cause problems later. You can't delete the fake package once it's released.