Add meaningful test of ppconvert in cmake

[correaa]

@markdewing @prckent

Please add numdiff -a 0.0001 ../build/src/QMCTools/ppconvert/test/Oxygen/O.BFD.xml ../tests/solids/monoO_1x1x1_pp/O.BFD.xml or equivalent to the tests, (with dependency or as part of ppconvert_does_not_crash). I don't know how to do this.

Is your feature request related to a problem? Please describe.
This complements ppconvert_does_not_crash. Comparing with a gold file (O.BFD.xml) is the only meaningful test of `ppconvert.
Currently it is only tested manually.

Describe the solution you'd like

Add to ctest, and also consider making -DBUILD_PPCONVERT=1 the default for cmake (if not already).

Describe alternatives you've considered

Running commands manually

Additional context

This is part of the refactoring of ppconvert to get rid of Blitz.
Some first steps towards this was done here: #2904