check elevation of highest pressure level in initialization

[ArcticSnow]

In the case the user misses pressure level high enough in the climate forcing dataset, the problem is identified only at the downscaling step. We can add a small check in the topoclass object initialization checking we have sufficient pressure levels.

• check elevation of the highest pressure levl against highest DEM elevation (Zplevel > Zdem)
• implement an ERROR statement suggesting which pressure level to get.

for task 1: check the $min(Z_{highest plevel} (x,y,time)) > max(Z_{dem}(x,y))$

[ealonsogzl]

I suppose that optionally the necessary pressure levels could even be obtained automatically from the DEM? It would avoid having to wait twice for the CDS queue if by mistake the right levels are not set.