Add constituent minimum values array interface

Description

Add interface to host cap to retrieve constituent minimum values array (for use by host model)

Solution

This should be a straight-forward update to

1. src/ccpp_constituent_prop_mod.F90: add new procedure field_min_value_ptr that returns a pointer to the minimum values array (vars_minvalue)
2. scripts/constituents.py: modify write_host_routines() to write a new routine (<hostname>_constituent_min_values).
3. scripts/host_cap.py: add the new routine name

The final generated code will look something like:

function <hostname>_constituent_min_values() result(min_values_ptr)

   ! Return pointer to minimum values array

   ! Dummy argument
   real(kind_phys), pointer :: min_values_ptr(:)

   min_values_ptr => <hostname>_constituents_obj%field_min_value_ptr()

end function <hostname>_constituent_min_values

Read src/ccpp_constituent_prop_mod.F90 and inspect the existing field pointer procedures, then follow write_host_routines() in scripts/constituents.py and the routine names in scripts/host_cap.py. Done means the minimum-values pointer interface and generated _constituent_min_values routine are available and return vars_minvalue as described.