Autoconfigure some of the b-tagging config flags

Properly configure b-tagging config flags to behave the same as in legacy config. This is done by defining ProductionStep.Derivation.

Also make JetFitterNN optional in PhysVal.

Marking urgent as we'd like to have it in the next release.

/cc @tstreble @jcatmore @calpigia @duperrin @thuffman @vdao @dguest @ywng