Add ability to preprocess non-GH evolution data

[knelli2]

Proposed changes

This allows codes that evolve BSSN or a variant of Z4 to dump the extrinsic curvature and auxiliary shift vector rather than the time derivative of the metric, lapse, and shift. We then compute these time derivatives instead, assuming 1+log slicing and the gamma-driver condition for the shift. If different lapse and shift conditions will be useful to the community, they can be added later but this should cover a large number of codes already.

Upgrade instructions

Code review checklist

• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.
• The PR lists upgrade instructions and is labeled bugfix or
  new feature if appropriate.

Further comments