Add headless options

[hmaarrfk]

Would benefit from: conda-forge/staged-recipes#25688

Closes #337

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.

[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.

[hmaarrfk]

@h-vetinari i'm not sure if you have the bandwidth to attempt: #365 again

It seems that there is some use of having multiple qt builds with opencv, and at least a headless build.

[hmaarrfk]

92 builds is somewhat riddiculous. we need a way to cut these down....

[hmaarrfk]

While I am not super excited about the 56 hour build time total build time (it should be closer to 6 if we could share the outputs well), it does address many grievances.

It does also give us the flexibility to remove the qt5 build readily when we feel we are ready for it.

A review would be greatly appreciated.

[h-vetinari]

@h-vetinari i'm not sure if you have the bandwidth to attempt: #365 again

Hm. Perhaps I can find some time to retry. But the multi-stage build process of opencv makes that really much much harder than I've seen for basically any other library. 🥲

[h-vetinari]

Looks very nice IMO, just a few questions/suggestions.