more changes for XIOS3

Some additional changes to provide fuller support for XIOS3

Compiling with key_xios3 permits NEMO to be compiled and run with XIOS3 but runtime warnings persist about deprecated functions and there are no demonstrators of the new XIOS3 features. In fairness, the new features are barely documented but this reference provides tantalising hints: Coupling workshop presentation

Code implementation

• The warnings can be suppressed with minor, key_xios3 protected, additions to iom.F90. These changes substitute some function calls:

xios_is_valid_extract_domain replaces xios_is_valid_zoom_domain
xios_set_extract_domain_attr replaces xios_set_zoom_domain_attr

• Corresponding changes need to be made to axis_def_nemo.xml, domain_def_nemo.xml and grid_def_nemo.xml:

extract_axis replaces zoom_axis
extract_domain replaces zoom_domain

These latter changes will be difficult to make to the SHARED copies without breaking XIOS2 compatibility

For now, changes to the xml files will be made in a new reference configuration containing local copies of any xml files with XIOS3-specific changes. This reference configuration will provide an example of a pool definition containing several services.

Documentation updates

Given the lack of XIOS3 documentation, it will be worth adding a section to the NEMO userguide covering the aspects most relevant to NEMO