Maintenance of the SAO component

Context

The compilation of the stand-alone observation operator (SAO) component of NEMO currently fails, in branches branch_4.2, branch_5.0, and main. The SAO source code (src/SAO/) has been designed to be co-compiled with the source code of the OCE component (src/OCE/): effectively, it replaces the central nemogcm.F90 file and makes use of other OCE modules. As the OCE source code has evloved, the SAO source code has not been kept in sync.

Proposal

It is proposed to restore the compilability of the SAO component, in particular to ensure the successful execution of

./makenemo -m <architecture> -r ORCA2_ICE_PISCES -n ORCA2_ICE_SAO -d "OCE ICE SAO" add_key "key_linssh" del_key "key_qco key_top"

in branches branch_4.2, branch_5.0, and main. Further, a review of the SAO source code is suggested, followed by any revisions that may result from such a review; it is also proposed to enable SETTE testing, and thus CI testing, of a test configuration that includes the SAO component in branch main.