Settle the question of SST definition in JEDI obs naming conventions

[twsearle]

Description

There is an open question about naming in the sea surface temperature processing. When we did the naming convention for JEDI we defined seaSurfaceTemperature as a variable. This is fine for our current processing as in situ temperature and potential temperature are identical at the surface. However, with the change to conservative temperature, the temperature is not the same as in situ temperature at the surface. Therefore we perhaps should add a seaSurfaceConservativeTemperature variable name.

In the SST configurations this is dealt with by overwriting the in situ temperatures with conservative temperature. This works adequately but is not particularly transparent. An alternative would be to not use seaSurfaceTemperature at all and just use waterTemperature and waterConservativeTemperature variable naming in the SST configurations, but this requires significant changes in the yaml.

This issue should be cross-referenced with a similar change in orca-jedi and jjdocs.

The issue was identified in http://fcm9/projects/utils/ticket/629

Acceptance Criteria (Definition of Done)

Settle a consistent approach to conservative sea surface temperature.