Allow choice of reading Pi and Phi from numeric ID

[knelli2]

Or setting them based on the 1- and 3-index constraints. Only works for numeric ID from GH vars. Numeric ID from ADM vars still computes phi with numerical derivatives.

Proposed changes

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

[nilsvu]

Note that Pi is always read from numeric ID, then modified to transform to the evolution gauge if SetPiAndPhiFromConstraints is true

[nilsdeppe]

LGTM!!! Thanks for doing this!!

The only possible thing we may want is the ability to set only pi, only phi, both, or none. However, I think that's beyond the scope of this PR and can be delayed until we need it. Probably the easiest way to generalize is to change the tag type from a bool to an enum with different states.

[knelli2]

Updated after discussions with @nilsvu. Decided that if we are reading GH numeric data, then we won't need to set Pi and Phi at all. Examples being PB&J and Ringdown. And if we are using ADM variables, we'll need to set Pi to work with the evolution gauge and set Phi to satisfy constraints. So I removed the option in the input file and now we just always set Pi and Phi from constraints unless we are using GH numeric ID