Build a model for debugging section for CICE5 can be updated

[anton-seaice]

The next deployments using CICE5:

ACCESS-NRI/ACCESS-ESM1.6#181

ACCESS-NRI/ACCESS-OM2#133

Now make it possible to configure the CICE5 block size directly in the spack environment (and can be done using the build-CD, without needing a local spack install).

The instructions https://docs.access-hive.org.au/models/build_a_model/build_source_code/#changing-number-of-processes-for-linaro-ddt can be updated to reflect this