Auxilliary fields added by default in 3D files

[rigoudyg]

By default, some auxiliary fields are added in 3D files (surface pressure for instance).
This addition should be made by default but it should be possible to skip it.
For pressure fields, the addition is not possible without the CMIP6 data request use and, even if it is used, it is not available at some time frequencies. This should be corrected.