MAINT: move `labels` configuration to `labels/` folder #304

Job	Run time
pytest / Determine job matrix	9s
style / Determine skipped pre-commit hooks	16s
doc / linkcheck / Check external links	49s
doc / nb / Execute and build documentation	55s
pytest / Run unit tests (3.10, ubuntu-22.04)	21s
pytest / Run unit tests (3.11, ubuntu-22.04)	23s
pytest / Run unit tests (3.7, ubuntu-22.04)	23s
pytest / Run unit tests (3.9, ubuntu-22.04)	22s
pytest / Run unit tests (3.6, ubuntu-20.04)	38s
pytest / Run unit tests (3.8, ubuntu-22.04, repoma)	28s
pytest / Run unit tests (3.9, macos-12)	1m 22s
style / Run local pre-commit hooks	46s
style / Run taplo through pre-commit	23s
doc / Upload to GitHub Pages	0s
style / Push changes	0s
	7m 15s

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