Create utility functions to allocate RIV/DRN/GHB cells

[JoerivanEngelen]

See this report from Sweco describing different methods to allocate cells with depth and distribute conductances over depth in iMOD5. Nice summary of requirements for this story!

20240129 Conductanceverdeling iMOD5.docx

I translated the list of settings in iMOD5.6 briefly below. We could create a set of utility functions to support this, so that users can mix and match what they'd like.

Allocation RIV cells with depth:

• Laying inbetween river stage and bottom elevation (IDEFFLAYER=0)
• First active cell to bottom elevation (IDEFFLAYER=-1)
• First active cell to bottom elevation, cells above river stage can only drain (IDEFFLAYER=1)
• In cells where bottom elevation is located (IDEFFLAYER=2)