To configure basic butler support for HEALPix, allowing reference catalogs and other prerequisite inputs to use HEALPix dimensions in the same way we currently support HTM, we just need to update the dimensions configuration by adding the following

skypix:

  healpix:

    class: lsst.sphgeom.HealpixPixelization

    max_level: 17

(leaving all other entries under the "skypix" heading as-is.

I don't think this change alone should actually affect the SQL schema, but our versioning logic knows that dimension configuration changes could affect the schema so I think it's best to treat it as a migration that happens to do nothing.