consider adding daf_butler

[hauntsaninja]

https://github.com/lsst/daf_butler
python/mypy#17002

[dhirving]

We'd love to be included in the regression test suite, since we already have a policy of tracking mypy releases immediately when they are released. We also have another repo that might be a good candidate: https://github.com/lsst/pipe_base

The two projects can be found on PyPI here:

• https://pypi.org/project/lsst-daf-butler/
• https://pypi.org/project/lsst-pipe-base/