feature: Allow filtering objects in templates thanks to labels

[pawamoy]

Is your feature request related to a problem? Please describe.

I'm working on a custom template for another project and I find myself in need to filter functions of a class based on their labels. Since I can't, and since I have to iterate twice on the functions, I have to use a condition on the labels twice.

Describe the solution you'd like

Probably add a parameter to filter_objects to accept labels. They should all be present, just like Griffe's Object.has_labels.

Describe alternatives you've considered

Checking labels in conditions.

Additional context

qtile/qtile#4612

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