MODERN_DIAG_MANAGER: fix error when setting zbounds for more than one variable

[uramirez8707]

Description
Fixes #1812
This PR includes two fixes to be able to support setting zbounds for more than one variable

1. This is only checking if the zbounds are the same. It should also be checking for the parent_axis_id.

   FMS/diag_manager/fms_diag_axis_object.F90

   Lines 1456 to 1467 in 59763e9

   	!< Determine if the axis was already created
   	axis_found = .false.
   	do i = 1, nfile_axis
   	select type (axis => diag_axis(file_axis_id(i))%axis)
   	type is (fmsDiagSubAxis_type)
   	if (axis%zbounds(1) .eq. zbounds(1) .and. axis%zbounds(2) .eq. zbounds(2)) then
   	axis_found = .true.
   	subaxis_id = file_axis_id(i)
   	exit
   	endif
   	end select
   	enddo

2. The dimension name is hard codded incorrectly:

   FMS/diag_manager/fms_diag_field_object.F90

   Line 1196 in 59763e9

   dimnames(i) = axis_ptr%axis%get_axis_name(is_regional)//"_sub01"

How Has This Been Tested?
CI, including the new test

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes