BUG: include ParameterSerializerConfig.cmake in SlicerExecutionModelConfig.cmake.

To fix Slicer linking with SlicerExecutionModel when linking against it so
that the location of ParameterSerializerLib is transitively propagated by the
inclusion of ParameterSerializerConfig.cmake -> inclusion of
ParameterSerializerTargets.cmake.

Clobbered the older JsonCppConfig.cmake because upstream has not included this
yet.