Address review comments for labels filtering

[jhrozek]

Summary

In the interest of time we merged labels filtering with some comments
not being addressed. This patch fixes that:

• exclude_labels now excludes any profiles containing any of the exclude
  labels. Add a test for this new behaviour.
• fix confusing comment in LabelsFromFilter
• special-case wildcard matching to only return the wildcard
• sort the slice in test to avoid issues where the slices contain the
  right elements, but in wrong order

Change Type

Mark the type of change your PR introduces:

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

make test

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 48.16% (+0.02%) from 48.143%
when pulling 40416ee on jhrozek:labels_comments
into 9a1a4ab on stacklok:main.