Add option to specify water_fp for PorousFlowBrine in PorousFlowFullySaturated

[hsheldon]

Motivation

Need to customise the FluidProperties UserObject for water to avoid P going out of range, e.g. by using tabulated fluid properties to extend the range of Water97. Currently if using PorousFlowBrine through the PorousFlowFullySaturated action there is no option to specify the water_fp that is used in PorousFlowBrine, hence it uses the default (I think this is Water97) which does not cover my required P range. Can achieve the desired outcome by specifying everything manually, but would prefer to use the action for simplicity.

Design

Add water_fp as an optional param for PorousFlowFullySaturated when using fluid_properties_type = PorousFlowBrine. Pass water_fp to PorousFlowActionBase::addBrineMaterial.

Impact

Should have no impact on validity of existing input files

[hsheldon]

@WilkAndy interested in your thoughts on this, maybe there was a reason why it wasn't done.

[cpgr]

It's possible that the water_fp param was added to PorousFlowBrine after the PorousFlowFullySaturated action was created and was never added there too?