imod_coupler ribamod/ribametamod: add logging stages via exchange collector

[Huite]

What If subgrid levels fall below MODFLOW elevations, the imod_coupler will not set the stage below the bed elevation.

This makes it hard to analyze afterwards what the actual used stages are.

Why To know exactly what stages are used in the MODFLOW computation.

How See DFM_MetaMod driver.