Krowgend add to factory water_oil_gas

[bartekvik]

This pull request proposes a solution for issue #455.

Issue The original issue reported that the current implementation of the WaterOilGas object did not allow for separate values of KROEND for water/oil and oil/gas systems. This is desirable in cases such as gas condensate systems and when oil moves into a gas cap. The issue includes examples and a figure to illustrate the problem.

Proposed solution The proposed solution is to accept both KROGEND (oil/gas) and KROWEND (water/oil) for the WaterOilGas object, then convert these into two separate KROEND and apply them to the respective WaterOil and OilGas objects. Thus, it does not affect anchoring of KROEND to critical and residual saturations. KROEND for WaterOil anchor to SWL, while KROEND GasOil anchor to SGCR=SGRO.
A test has been added to ensure this feature works.

Documentation No changes to the documentation have been made at this time. We will await approval of the proposed solution before updating the documentation.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.76%. Comparing base (ae09ae8) to head (62cf027).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #471   +/-   ##
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  Coverage   98.75%   98.76%           
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  Files          17       17           
  Lines        2725     2744   +19     
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+ Hits         2691     2710   +19     
  Misses         34       34           

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[berland]

Included in this PR there should be a corresonding update to the docs on https://equinor.github.io/pyscal/modelling.html