add XIOS3 compatibility
xios-3.0-beta is available since mid-2022. https://forge.ipsl.jussieu.fr/ioserver/browser/XIOS3/branches/xios-3.0-beta
We tested it in #93 and the first results are encouraging (better performance, reduce memory footprint...).
Switching from XIOS2.5 (trunk) to XIOS3 is quite transparent for NEMO. The only issue is that XIOS3 is not yet compatible with the tiles because, in XIOS3, they want to introduce tiles that will be compatible with OpenMP.
Note that New versions of Intel-MPI have issues with MPI_Probe. It is a know issue that has been fixed in mpich 4.0, see https://github.com/pmodels/mpich/pull/4731
Following what was done in 7ab53708, we will add a new cpp key
key_xiosthat will by-pass the calls to tile-specific XIOS2.5-trunk routines.